Tile Calculator
How much tile do you actually need? This free tile calculator gives DIYers and pro installers an instant materials list for any floor, wall, or full shower — tiles, thin-set bags sized by trowel and tile, grout in pounds and bags using the TCNA grout formula, waterproofing or uncoupling membrane (Ditra, Kerdi, RedGard, Hydro Ban), tile leveling clips, edge-profile sticks, and TCNA EJ171 movement joints with silicone tube counts.
Most tile calculators stop at square footage and a 10% waste guess. Real installations also need the right mortar class (A118.4 vs A118.15 medium-bed for LFT, A118.11 white for glass), the trowel size that hits 95% coverage in wet areas (ANSI A108.5), the correct grout type for the joint width (sanded ≥ 1/8", unsanded narrower, never sanded on glass or polished marble), and proper movement joints every 20–25 ft interior or 8–12 ft in wet/exterior — none of which a square-footage calculator can do.
Free, no signup. Outputs are pure materials — no labor cost, no $/sq ft pretending to be local. Cite TCNA Handbook 2024, ANSI A108/A118:2024, A137.1:2022, ASTM C373/C920, IPC, IRC R702.4. Always order from ONE dye lot to avoid shade variance (ANSI A137.1 §6.3 V0–V4).
Tile Calculator
Floor, wall, or full shower. Returns tiles, thin-set bags by trowel, grout (TCNA formula), waterproofing membrane, leveling clips, edge trim, and TCNA EJ171 movement joints with silicone tubes.
1. Where are you tiling?
Floor, wall, full shower, or freeze-thaw exterior. Drives wet-area rules + 95% coverage.
2. Dimensions
3. Tile material & size
Dense — back-butter LFT to reach 95% coverage. Slows modified-mortar cure.
Pick a preset or choose Custom to enter your own dimensions.
Tile with an edge ≥15″? See why large-format must stagger ≤33%
Used as joint depth — typical 1/4–3/8"
4. Pattern, joint & installer
Not sure how much pattern adds to waste? See the layout-pattern diagram
5. Substrate
CBU per A118.9 over a flat, fastened subfloor. Tape and thin-set all seams with 2" alkali-resistant mesh.
Tiling a shower or tub? See what goes behind the tile (never drywall)
How tile layout and substrate change what you buy
The square footage is the easy part. These engineering-style diagrams cover the three things that trip up most tile estimates: why the layout pattern — not just the area — sets your waste factor, why large-format tile has to be staggered ≤33% to avoid a raised lip, and what really goes behind shower tile (tile and grout are not waterproof on their own).
The layout-pattern comparison is why the calculator ties waste to your pattern, not a flat number. Angled and offset patterns throw away a cut at every wall, so a diagonal or herringbone floor wastes more than a straight lay. Picking the pattern is what sets the overage the estimate adds on top of the field.
The large-format diagram is why big tile changes both the offset and the mortar. Any tile with an edge over fifteen inches is large-format and must be staggered less than a third of its length, not a half, so the joints stay off the slightly crowned center and avoid lippage. It also sets with medium-bed mortar at high coverage, which the calculator accounts for.
The wet-wall assembly is why a shower estimate is a stack of layers, not just tile and thin-set. Tile and grout are not waterproof — the membrane behind them is — so the wall goes framing, cement board, waterproofing membrane, thin-set, then tile. Those substrate and membrane layers are separate materials the calculator includes.
Calculation Formulas
Industry grout formula. L and W are tile dimensions in inches; JW = joint width; JD = joint depth (≈ tile thickness); K = grout density (lbs/ft³) ÷ 12. K=8.33 for Laticrete-aligned 100 lb/ft³ cement grout; K=9.00 for Custom Building Products Polyblend at 108 lb/ft³. Calculator uses K=8.67 as a defensible middle value verified by back-calculation against both manufacturers' published coverage tables.
Example:
12×24 porcelain at 3/16" joint × 3/8" depth: ((24+12)/(24×12)) × 0.1875 × 0.375 × 8.67 = 0.076 lbs/sq ft. 200 sq ft = 15.2 lbs + 10% mix loss → 17 lbs → one 25 lb bag.
Laticrete's published 10% baseline plus pattern, large-format, and natural-stone adders. Pro vs DIY differs by 3–5 percentage points. Pattern matrix: straight 7% pro / 12% DIY; running bond 10/13; diagonal 15/18; herringbone 15/20; Versailles 15/20. Always +5pp for LFT and +5pp for natural stone.
Example:
200 sq ft floor with 12×24 porcelain in 1/3 offset, pro install: 10% baseline + 5pp LFT = 15%. 200 × 1.15 = 230 sq ft of tile to order.
Tile face area = (L × W) ÷ 144 sq in/sq ft. Boxes round up to the next whole carton — and you should buy from ONE dye lot to avoid shade variance (ANSI A137.1 §6.3 V0–V4).
Example:
230 sq ft of 12×24 porcelain: 230 ÷ 2 sq ft = 115 tiles. At 8 tiles per 16 sq ft carton → 15 boxes.
TCNA F115/F116 selects trowel by max tile dimension. Mapei FAQ coverage: 1/4×1/4 ~80–100 sq ft/50 lb bag; 1/4×3/8 ~60–80; 1/2×1/2 ~40–50. Multiply by 0.85 for wet areas (95% coverage requirement) or for back-buttering large-format tile. Multiply by 0.67 when embedding radiant cable.
Example:
230 sq ft, 12×24 tile (1/2×1/2 trowel, 45 sq ft/bag), wet area: 45 × 0.85 = 38 sq ft/bag effective. 230 ÷ 38 = 6.1 → 7 bags.
Verbatim ANSI A108.5: "average uniform contact area shall be not less than 80% except on exterior or shower installations where the contact area shall be 95% when no less than three tiles or tile assemblies are removed for inspection." Natural stone TCNA: 95% minimum in all areas with no voids exceeding 2 sq in and no voids within 2" of tile corners.
Example:
Shower wall tile: 95% coverage required. If first pull-test shows 70% contact, you are non-compliant — switch to bigger notch + back-butter.
RedGard meets ANSI A118.10 at 40 sq ft/gal wet (93 mil), TWO coats; meets A118.12 crack-iso at 50 sq ft/gal each, two coats. Schluter Kerdi rolls = 108 sq ft; bond with Schluter-approved unmodified or ALL-SET. Apply +5% overlap factor for sheet seams.
Example:
Full shower with 60 sq ft pan + walls + curb + niche: RedGard waterproof = 60 × 2 / 40 = 3 gallons.
Required at every restraining surface — walls, columns, curbs, dissimilar floors. Width ≥1/4" interior perimeter, ≥3/8" exterior at 8 ft, ≥1/2" exterior at 12 ft. Silicone must meet ASTM C920 Class 25 minimum (Class 50 if calculated movement exceeds 25% of joint width per ASTM C1193).
Example:
20 ft × 12 ft wet area, 1/4" joint: perimeter 64 LF + 2 field joints × 12 ft = 88 LF. 10.1 oz tube at 1/4" flat ≈ 24 LF → 4 tubes.
Schluter JOLLY / RONDEC / RENO-U / SCHIENE / QUADEC standard stock length is 8' 2-1/2" (98.5" / 2.5 m). Some finishes also stocked in 10' (120"). Bullnose tile is normally 6" long.
Example:
22 LF of exposed edge with Schluter JOLLY: 22 × 12 / 98.5 = 2.68 → 3 sticks.
Stricter flatness avoids lippage on large-format tile. Check with a 10-ft straightedge — gaps to be filled with self-leveler before installation. ANSI lippage allowance: 1/32" for joints 1/16–<1/4", 1/16" for joints ≥1/4", plus tile's allowable warpage.
Example:
12×24 plank LFT install: floor must be flat within 1/16" over any 2 ft span. If not, pour SLU before tiling.
Cable kits sold in fixed sizes (e.g., Ditra-Heat 21/32/43/60/85/120 sq ft). Never run cable under cabinets, tubs, or toilets. Thinset coverage drops to ~67% of normal because mortar must fully encapsulate the wire (no air pockets).
Example:
80 sq ft bathroom minus 18 sq ft vanity & toilet footprint = 62 sq ft open. Order 85 sq ft cable kit + 65 sq ft membrane.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| Grout density (cement) | 100–110 lbs/ft³ | Laticrete PermaColor ~100; CBP Polyblend ~108. K = density ÷ 12 → 8.33–9.00 for the grout-volume formula. |
| Large-format threshold | ≥15 inches | Any tile with one edge ≥15" per ANSI A108.02-2023 §4.5.2 — triggers medium-bed mortar, 33% offset max, and tighter substrate flatness. |
| Mortar coverage — dry interior | 80% minimum | ANSI A108.5 §3.3.2 — averaged across at least 3 lifted tiles. |
| Mortar coverage — wet/exterior | 95% minimum | ANSI A108.5 §3.3.2 — applies to showers, tub surrounds, and all exterior installations. |
| Mortar coverage — natural stone | 95% everywhere | TCNA Handbook — no voids exceeding 2 sq in and no voids within 2" of corners. |
| Substrate flatness — standard | 1/4" in 10 ft | ANSI A108.02-2023 §4.2 for tile <15" edge. Also 1/16" in 1 ft. |
| Substrate flatness — LFT | 1/8" in 10 ft | ANSI A108.02-2023 §4.2 for tile ≥15" edge. Also 1/16" in 2 ft. |
| Movement joint spacing — interior | 20–25 ft o.c. | TCNA EJ171 each direction, plus all perimeter & plane changes. |
| Movement joint spacing — wet/exterior | 8–12 ft o.c. | TCNA EJ171. Minimum joint width 3/8" at 8 ft o.c., 1/2" at 12 ft. |
| RedGard coverage — A118.10 | 40 sq ft/gal × 2 coats | Custom Building Products TDS-104, 93 mil wet. Two coats required for waterproof rating. |
| Schluter profile length | 98.5 in (8' 2-1/2") | Standard JOLLY/RONDEC/SCHIENE/QUADEC/RENO-U stock length; some SKUs also 10 ft. |
| Shower pan slope minimum | 1/4" per foot | International Plumbing Code minimum slope to drain. Required under both pre-slope and final mortar bed. |
| Tile shade variation | V0–V4 | ANSI A137.1 §6.3 classifies shade variation. V0 = uniform; V4 = substantial random — always order from one dye lot. |
| Porcelain absorption (ANSI A137.1) | ≤0.5% (impervious) | ASTM C373-18 boil-soak weight-gain test classifies tile: impervious ≤0.5%, vitreous ≤3%, semi-vitreous ≤7%, non-vitreous >7%. |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
TCNA Handbook for Ceramic, Glass, and Stone Tile Installation (2024)(TCNA Handbook 2024)
View StandardIndustry-standard reference for tile installation in North America. Codifies installation methods (F-series for floors, W-series for walls, B-series for backings, EJ171 for movement joints) with substrate requirements, mortar selection, and shower assembly details.
Key Requirements:
- •Mortar coverage: 80% dry interior, 95% wet/exterior, 95% natural stone everywhere
- •Floor methods: F141 plywood subfloor minimums, F144 backer board over ply, F125 crack-isolation over concrete, F250 stone over wood
- •Wall methods: B414 (cement board) and B415 (coated glass-mat); greenboard NOT permitted in wet areas
- •EJ171 movement joints: 20–25 ft interior, 8–12 ft wet/exterior, all perimeter & plane changes
- •Shower pre-slope: 1/4 inch per foot to drain; final mortar bed 1/2" thick at drain on slab, 3/4" on wood
ANSI A108 / A118 / A136.1 / A137.1 Installation & Material Standards (2024)(ANSI A108/A118/A136.1/A137.1:2024)
View StandardThe companion to the TCNA Handbook. A108 covers installation specifications (workmanship, coverage, lippage); A118 covers material classifications (modified vs unmodified thinset, sanded vs unsanded grout, membranes); A137.1 classifies tile quality and shade variation.
Key Requirements:
- •A108.5 §3.3.2 — 80% / 95% mortar contact rule
- •A108.02-2023 §4.5.2 — large-format ≥15" edge: max 33% offset, joint width minimums
- •A118.4 modified thinset; A118.15 LHT/medium-bed (LFT); A118.11 EGP (plywood); A118.3 epoxy; A118.10 waterproof membrane; A118.12 crack-isolation membrane
- •A118.6 standard cement grout (sanded/unsanded), A118.7 polymer-modified, A118.3 epoxy
- •A137.1 §6.3 — shade variation V0 (uniform) through V4 (substantial random)
ASTM C373-18 — Water Absorption Test(ASTM C373-18)
View StandardStandard test method for determining a tile's water absorption by boiling/soaking and measuring weight gain as a percentage of dry weight. The basis for porcelain vs ceramic classification under ANSI A137.1.
Key Requirements:
- •Impervious (porcelain): ≤0.5% — suitable for freeze-thaw exterior
- •Vitreous: >0.5% to 3%
- •Semi-vitreous: >3% to 7%
- •Non-vitreous: >7% — NOT for exterior freeze-thaw
ASTM C920-18 — Elastomeric Joint Sealants(ASTM C920-18 / ASTM C1193)
View StandardSpecification for single-component sealants in movement joints. Movement classes 12.5, 25, 35, 50, and 100/50 describe the percentage of joint width the sealant can accommodate without failure. C1193 covers joint design and movement calculation.
Key Requirements:
- •Movement Class 25: ±25% joint width (entry-level for tile movement joints)
- •Movement Class 50: ±50% (upgrade when calculated movement exceeds 25% per C1193)
- •Traffic-area sealants: Shore A hardness ≥25
- •100% silicone required for tile movement joints (NOT acrylic latex caulk)
International Plumbing Code (IPC) — Shower Pan Slope(IPC 417.5 / IRC P2709)
View StandardPlumbing code minimum slope for shower pans to drain — required under both the pre-slope (under the liner) and the final mortar bed.
Key Requirements:
- •Minimum slope: 1/4 inch per foot to drain
- •Pre-slope required under all liner/membrane systems (clamping-ring drains) so water reaches weep holes
- •Final mortar bed minimum 1/2 inch thick at the drain on slab, 3/4 inch on wood subfloor
- •ALL horizontal surfaces in a shower — niche shelves, curbs, benches — must also slope to drain
International Residential Code (IRC) R702.4 — Wet-Area Tile(IRC R702.4 (2024))
View StandardResidential building code requirements for tile installation in wet areas including showers, tub surrounds, and steam rooms. Mandates thinset (not mastic), backer over fasteners, and approved membranes.
Key Requirements:
- •Walls in wet areas: cement board (ANSI A118.9) or fiber-cement, glass-mat coated, or fiber-mat-reinforced gypsum
- •Standard gypsum board PROHIBITED in showers and tub surrounds
- •Adhesives: Type I mastic acceptable for dry-area walls only; wet areas require thinset
- •Waterproof membrane (A118.10) required at all shower walls/floor or behind tile
NTCA Reference Manual(NTCA Reference Manual)
View StandardNational Tile Contractors Association installation reference. Companion to the TCNA Handbook with practical installation guidance, pre-install checklists, and troubleshooting for grout failures, lippage, and tile cracking.
Key Requirements:
- •Substrate moisture verified by ASTM F2170 before installation over concrete
- •Deflection: L/360 for ceramic/porcelain; L/720 for natural stone; L/480 for LFT over wood
- •Mockups recommended for offset patterns ≥33% on LFT to verify lippage acceptance
- •Leveling clips recommended for LFT and polished tile to control lippage under wall-wash lighting
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
Freeze-Thaw Exterior Tile
ASTM C373 absorption + ANSI A137.1 frost rating
Only impervious tile (≤0.5% water absorption per ASTM C373-18) is rated for freeze-thaw exterior. Non-vitreous ceramic and porous natural stone crack in cold climates as absorbed water freezes and expands.
Regional Examples:
Slab Moisture & Crack-Isolation Over Concrete
TCNA F125 + ANSI A118.12 — Avoid the #1 cause of tile failure on slabs
Concrete slabs move (curing shrinkage, thermal cycling, settlement) and transmit cracks into tile. ANSI A118.12 crack-isolation membranes (Ditra, RedGard at 50 sq ft/gal, Hydro Ban) bridge cracks up to 1/8". Slab moisture content per ASTM F2170 should be verified before tile.
Regional Examples:
Wet Area Code Differences (Showers / Tub Surrounds / Steam)
IRC R702.4 + local code overlays
Code-required wet-area assemblies differ by jurisdiction. Standard drywall is prohibited in all showers (IRC R702.4) but greenboard rules vary. Steam showers require continuous waterproofing on walls AND ceiling.
Regional Examples:
Seismic Zones — Movement Accommodation
TCNA EJ171 in seismic regions
Seismic activity puts additional stress on rigid tile assemblies. Cities in Zone D/E (California, PNW, Anchorage) often require closer movement joint spacing, wider joints, and Class 50 sealants in commercial.
Regional Examples:
Substrate Choices Vary by Region
Plywood vs concrete vs steel-stud — different prep
What's behind your tile differs by region: West Coast slab-on-grade, Northeast plywood-over-joists, commercial steel stud. Each substrate has different deflection, fastening, and membrane needs.
Regional Examples:
Material Selection by Climate & Use
Porcelain dominates US new construction; ceramic and stone niche
Porcelain has become the default in new US residential construction (62% of the market per TCNA economic data) because it works in all climates, on all substrates, and meets every code. Ceramic and natural stone remain regionally and aesthetically driven.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
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How to Use This Calculator
- Pick application: floor (dry or wet), wall (dry or wet), full shower (pan + walls + curb + niche + bench + optional ceiling), or freeze-thaw exterior.
- Enter dimensions: rooms (length × width) for floors; walls (length × height, less openings) for walls; pan/wall/door/niche/curb/bench dimensions for showers.
- Choose a tile material (porcelain, ceramic, glass, marble, travertine, slate, limestone, cement, mosaic, metal) and a size preset — or enter custom width/length/thickness. Check the polished box if it matters (forces unsanded grout on marble/glass/metal).
- Pick a layout pattern (straight stack, running bond, diagonal, herringbone, basketweave, Versailles, modular), grout joint width (1/16 to 3/8 inch), and installer experience (pro vs DIY).
- Select the substrate (concrete, plywood, cement board, Ditra, existing tile, or drywall for non-wet walls only).
- Open the advanced sections if relevant: waterproofing/uncoupling membrane (Ditra, Kerdi, RedGard, Hydro Ban, AquaDefense), heated floor cable + uncoupling, edge trim profiles (Schluter JOLLY/RONDEC/RENO-U/SCHIENE/QUADEC or bullnose), and TCNA EJ171 movement joints + leveling clips.
- Click Calculate: get tiles + boxes (rounded to one dye lot), thin-set bags by trowel, grout bags from the TCNA formula, membrane rolls or gallons, edge-trim sticks, silicone tubes for movement joints, plus installation notes and warnings.
How the TCNA grout formula and coverage rules work
The grout formula is: lbs/sq ft = ((L + W) / (L × W)) × joint width × joint depth × K. The K constant is the grout density in lbs/ft³ divided by 12 — K = 8.33 for Laticrete cement grouts (≈100 lb/ft³) and K = 9.00 for Custom Building Products Polyblend (≈108 lb/ft³), both back-verified from published coverage tables. The calculator uses K = 8.67 as a defensible mid-range. Thin-set coverage is driven by trowel notch size and tile dimension per TCNA F115/F116, then reduced 15% for wet areas (to hit the ANSI A108.5 95% coverage rule) and further reduced ~33% when embedding heated-floor cable. Always back-butter any tile with one edge ≥15 inches (large format / LFT) per ANSI A108.02-2023 §4.5.2, which also forces 33% max offset and ≥1/8" rectified joints.
Frequently Asked Questions
How much thinset do I need per square foot of tile?
Trowel size drives coverage, and trowel size is selected by tile dimension per TCNA F115/F116. Per the Mapei FAQ and confirmed against Custom Building Products and Laticrete: a 1/4"×1/4" square notch (for 4–8" tile) covers ~80–100 sq ft per 50 lb bag; 1/4"×3/8" (for 8–12") covers ~60–80; 1/2"×1/2" (for 12"+ / large-format) covers ~40–50. Reduce coverage by ~15% in wet areas to hit the ANSI A108.5 §3.3.2 95% coverage rule, and reduce another ~33% (i.e. budget ~1.5× material) when embedding radiant cable so the wire is fully encased. For a 200 sq ft floor of 12×24 porcelain in a dry interior: 200 / 45 ≈ 5 bags.
How much grout do I need for 12×24 tile?
Use the TCNA grout formula: lbs/sq ft = ((L + W) / (L × W)) × joint width × joint depth × K. K is the grout density (lbs/ft³) divided by 12 — K = 8.33 for Laticrete cement grouts (≈100 lb/ft³) and K = 9.00 for Custom Building Products Polyblend (≈108 lb/ft³). Both values are verified by back-calculation against the manufacturers' published coverage charts. For 12×24 tile at 3/16" joint × 3/8" depth: ((24+12)/(24×12)) × 0.1875 × 0.375 × 8.67 = ~0.076 lbs/sq ft. 200 sq ft = ~15 lbs of grout + 10% mix loss = ~17 lbs, which is one 25 lb bag. Aggregator densities of 0.1875 lbs/in³ (= 324 lbs/ft³) circulating online are about 3× too high — do not use.
What waste factor should I order for tile?
Laticrete's published baseline is 10% minimum for any tile job — and that is the floor, not the ceiling. Add to it: pattern complexity (running bond / brick: 10% pro / 13% DIY; diagonal: 15% / 18%; herringbone: 15% / 20%; Versailles or modular mosaic: 15% / 20%), large-format (any edge ≥15"): +5pp, natural stone: +5pp, polished tile: +2pp. So a DIY herringbone porcelain floor lands around 25%, while a pro straight-lay 12×12 floor lands at 10%. Always order on-spec or above — running short risks dye-lot mismatch (ANSI A137.1 §6.3 V0–V4) since manufacturers rarely guarantee a same-lot reorder.
Do I need modified or unmodified thinset over Ditra and Kerdi?
This is the most contested question in tile. Schluter's position (controlling for warranty purposes): use UNMODIFIED A118.1 dry-set to bond tile TO Ditra or Kerdi, because an impervious membrane sandwiched with impervious tile traps water in modified mortar and slows cure to 14–60 days per TCNA. To bond Ditra TO plywood you DO need modified A118.11. Schluter's own ALL-SET mortar (modified, meets A118.4T / .11 / .15) is permitted within the system. ANSI's position (A118.12 covers crack-isolation membranes used with modified mortar): modified mortar works, but the slow-cure issue is real. Bottom line: follow Schluter's manual to keep the system warranty, or use ALL-SET if you want one bag that does both layers.
What size trowel do I need for large-format tile (12×24 and bigger)?
Per TCNA F115/F116, any tile with one edge ≥15" is large-format (LFT) and triggers ANSI A108.02-2023 §4.5.2: medium-bed mortar (A118.15) once the embedded thickness exceeds 3/16", a 1/2"×1/2" or larger square-notch trowel, mandatory back-buttering, and 33% max offset. Substrate flatness tightens from 1/4" in 10 ft (standard) to 1/8" in 10 ft AND 1/16" in 2 ft. For 24"+ tile you'll typically run a 3/4"×3/4" square notch at ~30 sq ft per 50 lb bag. Back-buttering and the 95% wet-area coverage rule (ANSI A108.5 §3.3.2) effectively cut coverage another ~15%.
Can I use sanded grout with glass tile?
No. Sanded grout will scratch the surface of glass, polished marble, polished metal, and any honed or polished natural stone. Use unsanded grout (joints up to 1/8") or epoxy grout (ANSI A118.3) for wider joints. Glass tile also requires WHITE thinset (A118.4 white or A118.11 white) regardless of joint width, because glass is translucent and gray thinset will show through. For wider glass-tile joints (3/16"+), epoxy grout is the only correct answer.
How much RedGard or Kerdi do I need for a shower?
RedGard is sold by the gallon; coverage depends on which ANSI standard you're meeting. Per Custom Building Products TDS-104: for A118.10 waterproof rating, apply at 40 sq ft per gallon at 93 mil wet (47 mil dry), TWO coats — so a typical 80 sq ft shower needs 4 gallons. For A118.12 crack-isolation only, apply at 50 sq ft per gallon per coat, two coats. Schluter Kerdi sheet membrane comes in 108 sq ft rolls (3'3" × 33'); the same 80 sq ft shower needs 1 roll plus a roll of Kerdi-Band for seams. Showers require an A118.10 waterproofing membrane by code (IRC R702.4) — A118.12 crack-iso alone is NOT a waterproof rating.
Where do tile movement joints go and how often?
Per TCNA EJ171: interior floors get joints every 20–25 ft in each direction; exterior or wet areas every 8–12 ft. ALWAYS at the perimeter (where tile abuts walls, columns, curbs, dissimilar floors), at every change of plane (inside corners), and through any existing substrate control joints. Joint width minimum: 1/4" interior perimeter (never less than 1/8"), 3/8" exterior at 8 ft o.c., 1/2" at 12 ft o.c. Fill with 100% silicone meeting ASTM C920 Class 25 (Class 50 if calculated movement per ASTM C1193 × 1.25–1.5 safety factor exceeds 25% of joint width). A 10.1 oz tube covers about 24 LF at a 1/4" flat fill.
What's the difference between A118.4 modified thinset and A118.15 medium-bed?
Both are polymer-modified, but A118.15 (also called LHT or medium-bed) has a stiffer mix that holds up to 3/4" thickness without sagging — critical for large-format tile that needs back-buttering and a thicker bed to achieve 95% coverage on the inevitable lippage. Standard A118.4 sags at thicknesses over ~3/16" and is fine for tile under 12". The Custom Building Products LFT FAQ is explicit: "Use medium-bed mortar for tile with one edge greater than 15 inches when the embedded mortar thickness exceeds 3/16 inch." For 12×24 or anything bigger, switch to A118.15 — A118.4 alone leaves voids.
Do I need tile leveling clips, and how many per square foot?
Leveling clip systems (Raimondi RLS, Spin Doctor, Tuscan) are not optional for: large-format tile (any edge ≥15"), polished tile (lippage shows brutally under wall-wash lighting), plank patterns over 12" long (warpage), and 50% offsets of any large tile. Coverage per Raimondi guidance via Tools4Flooring: ~2 clips per square foot for 12×12 and larger, plus ~25% wedges. Plank tile gets ~2 clips per long joint + 1 per short joint. ANSI A108.02-2023 §4.4 caps lippage at 1/32" for joints 1/16"–<1/4" and 1/16" for ≥1/4" joints, plus the tile's own allowable warpage — clips are how you actually hit those tolerances.
What grout joint width should I use?
Tile manufacturer spec governs, but the practical defaults: rectified porcelain takes 1/16"–1/8"; pressed-edge ceramic typically 3/16"; large-format and natural stone need 3/16"–1/4" to absorb edge warpage; handmade or rustic tile often 3/8". ANSI A108.02-2023 sets a hard minimum of 1/8" for any rectified tile with one edge >15" (3/16" if calibrated), and the joint must increase by the tile's edge warpage. The grout type follows: sanded for joints ≥1/8" (ANSI A118.6 sanded); unsanded for joints up to 1/8" — except on glass, polished marble, and metal, which never take sanded grout regardless of joint width.