Grout Calculator
How much grout do you actually need? This free grout calculator gives DIYers and tile setters an instant answer — pounds, 25-lb bags, small boxes, or epoxy Full Units — from just your tile size, joint width, joint depth, and area. It uses the dimensionally-correct perimeter-to-area coverage formula, not a shortcut that bakes in a fixed tile thickness.
Grout coverage swings enormously with tile size and joint width: a single 25-lb bag covers roughly 54 sq ft of 1×1 mosaic but over 340 sq ft of 12×12 floor tile. That is because smaller tiles pack far more joint length into every square foot. The calculator also checks your grout type against your joint — sanded for joints over 1/8", unsanded at or below, epoxy for wet and commercial areas — so you don't buy a product that shrink-cracks or scratches your tile.
Built on ANSI A108.02 (joint width), A108.10 (full-depth fill), A118.6 (sanded vs unsanded), A118.3 (epoxy), and the TCNA Handbook, with densities back-calculated from real manufacturer coverage charts. Materials only — no pricing, no labor. Free, no signup.
Grout Calculator
Calculate how much grout you need — bags, boxes, or epoxy units — from your tile size, joint width, and area, using the TCNA / ANSI perimeter-to-area coverage formula.
Tile
Why do small tiles need so much more grout than large ones? See the coverage diagram
Tile thickness is the grout joint depth (joints are filled full-depth per ANSI A108.10). Typical: glass mosaic 1/8"–1/4", ceramic wall 1/4"–5/16", porcelain floor 5/16"–3/8", natural stone 3/8"+.
Why does tile thickness matter? See how grout fills the joint full-depth
Joint & area
Not sure? Calculate your square footage →
Minimum joint is 1/16" and at least 3× the tile's facial-dimension variation (ANSI A108.02 §4.3.8).
Grout type & waste
Unsanded for joints 1/16"–1/8" (and polished stone / glass); sanded for 1/8"–1/2"; epoxy for wet, commercial, and chemical-exposure areas (sold by kit, never needs sealing).
Sanded, unsanded, or epoxy? See which grout your joint width calls for
What actually drives how much grout you buy
A grout take-off surprises people because it doesn't track square footage the way paint or thin-set does. These engineering-style diagrams show why tile size — not just area — is the biggest driver, how the joint is a full-depth channel so your tile thickness matters, and how joint width decides whether you buy unsanded, sanded, or epoxy grout.
The tile-size comparison is why grout is not a flat per-square-foot number. Small tiles pack far more joint length into the same area than large tiles, so a mosaic can use many times the grout of a big tile at the same joint width. That is why the calculator asks for tile size, not just the area to grout.
The joint cross-section explains why tile thickness drives grout volume as much as joint width. Grout fills the joint full-depth, so each joint is a channel — width times depth times length — and depth equals the tile thickness. A thick floor tile therefore uses far more grout than a thin mosaic at the same joint, which is why thickness is an input.
The type-selector is why the calculator ties grout type to joint width and exposure. Unsanded suits narrow joints and delicate faces, sanded is the wider-joint floor workhorse, and epoxy handles wet or chemical areas — and the type changes how it is sold and whether it is sealed. Picking by joint width is what keeps the joint from cracking or the tile from scratching.
Calculation Formulas
The dimensionally-correct coverage formula. (L+W)/(L×W) is the perimeter-to-area ratio (joint length per unit area); Jw × Jd is the joint cross-section; A is area in sq ft; K = (144/1728) × ρ folds in the unit conversions and grout density. Reproduces every major manufacturer coverage chart.
Example:
12×12×3/8" tile, 1/8" joint, 100 sq ft, sanded (ρ≈110): 0.16667 × 0.125 × 0.375 × 100 × 9.2 ≈ 7.2 lb — one small box.
Linear inches of grout joint per square inch of surface. This is WHY tile size drives grout use: perimeter falls linearly with tile size while face area falls with the square, so the ratio rises sharply as tiles shrink.
Example:
A 1×1 mosaic has P/A = 2.0/in; a 12×12 tile has 0.1667/in — 12× more joint length per square foot.
Multiply the per-square-inch joint cross-section by 144 in²/ft² to get cubic inches of grout per square foot of installed tile.
Example:
12×12×3/8" tile at a 1/8" joint: 0.16667 × 0.125 × 0.375 × 144 = 1.125 in³ per sq ft.
Convert cubic inches of joint volume to cubic feet, then multiply by grout bulk density ρ (lb/ft³). Density is back-calculated from coverage charts: ρ≈99–100 for Laticrete/MAPEI/ARDEX, ρ≈110 for Custom Building Products.
Example:
100 sq ft × 1.125 in³ = 112.5 in³ = 0.0651 ft³ → ×100 = 6.5 lb (Laticrete basis) or ×110 = 7.2 lb (CBP basis).
A thinner tile can still use MORE grout if it is smaller, because the perimeter-to-area ratio dominates. The size effect usually outweighs the thickness effect.
Example:
3×6×1/4" subway at 1/8" joint = 2.25 in³/sq ft — nearly 2× the 12×12×3/8" tile (1.125 in³/sq ft) despite being thinner, because its P/A ratio is 3× larger.
Per MAPEI/Laticrete/NTCA, add 10% for mixing loss, sponge cleanup, partial-bag rounding, and joint-width variation. Bump to 12–15% for porous/unglazed/quarry tile and mosaics, or down to 5% for clean pro straight-lay.
Example:
7.2 lb raw × 1.10 = 7.9 lb to buy.
Cementitious grout is sold in 7/8/10 lb boxes and 25 lb bags — round up to whole units. Epoxy is sold by kit/unit volume, not weight: divide total joint volume by the Full-Unit yield (188.9 in³ for SPECTRALOCK) and round up.
Example:
7.9 lb → one 10 lb box (or one 25 lb bag for a bigger job). 225 in³ of epoxy ÷ 188.9 = 2 Full Units.
The common shortcut drops the joint-depth (Jd) term, forcing the constant 1.888 to absorb a fixed tile thickness of ≈0.227". It is accurate only near that thickness — it under-predicts ~40% for 3/8" floor tile and over-predicts ~80% for 1/8" mosaics. This calculator uses Formula A with tile thickness as a real input.
Example:
1.888 ÷ (0.08333 × 100) = 0.227" — the hidden tile thickness baked into Formula B.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| K Factor | K = (144/1728) × ρ = 0.08333 × ρ | Composite unit-conversion-times-density constant in Formula A. K ≈ 8.25 (Laticrete/MAPEI, ρ≈99) to 9.2 (CBP, ρ≈110). Both codebase values are correct — they reflect different assumed densities, not a math error. |
| Sanded Grout Density | ρ ≈ 99–110 lb/ft³ (default 110) | Back-calculated from 25-lb coverage charts. We default to the conservative high end (CBP basis, K≈9.2) so the tool never under-buys; selecting a lower-density product yields a slightly lower number. |
| Unsanded Grout Density | ρ ≈ 90–100 lb/ft³ (default 100) | Unsanded cementitious grout runs slightly less dense than sanded. Rated for 1/16"–1/8" joints only. |
| Epoxy Full-Unit Yield | 188.9 in³ per Full Unit | From the LATICRETE SPECTRALOCK PRO Premium coverage data. 1 Full Unit = 4 Mini Units. Epoxy is computed by volume → units, never reported in pounds. |
| Minimum Joint Width | 1/16" (and ≥ 3× facial variation) | ANSI A108.02 §4.3.8: the grout joint must be at least 3× the tile's actual facial-dimension variation and never less than 1/16". Tiles > 15" in running-bond need 1/8" (rectified) or 3/16" (calibrated). |
| Sanded vs Unsanded Threshold | 1/8" joint | Per ANSI A118.6, use sanded grout for joints wider than 1/8" (the sand resists shrinkage cracking) and unsanded for joints 1/8" and narrower. Unsanded is also required on scratch-sensitive polished stone and glass. |
| Default Waste Factor | 10% | MAPEI/Laticrete/NTCA consensus. Covers mixing/bucket loss, sponge cleanup, partial bags, and joint-width variation. 12–15% for porous/unglazed/mosaic; 5% for clean pro straight-lay. |
| Bag & Unit Sizes | 7 / 8 / 10 lb boxes, 25 lb bags; epoxy by kit | CBP Polyblend Plus: 7 lb box + 25 lb bag. Laticrete PermaColor: 8 / 25 lb. MAPEI Ultracolor Plus FA: 10 / 25 lb. ARDEX FH: 10 / 25 lb. Epoxy: Mini / Full / Commercial units. Always round up. |
| Full-Depth Joint Assumption | Jd = tile thickness | ANSI A108.10 §5.3.4 requires joints filled uniformly and full-depth. The calculator treats joint depth as tile thickness; if thinset partially fills the joint or the tile is gauged thin, actual grout use is slightly lower. |
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.
ANSI A108.02 — Joint Width & General Installation Requirements(ANSI A108.02)
View StandardThe installation standard that governs grout joint sizing. Sets the legal minimum joint width as a function of the tile's facial-dimension variation — the rule that determines how much grout a job actually consumes.
Key Requirements:
- •§4.3.8: actual grout joint ≥ 3× the actual facial-dimension variation of the tile supplied; never less than 1/16"
- •§4.3.8.1: tiles with any side > 15" in running-bond/brick patterns (> 33% offset) need a minimum 1/8" joint for rectified, 3/16" for calibrated tile
- •Verbatim example in the standard: 1/16" total facial variation → 3/16" minimum joint
- •Joint width may vary across a job to absorb tile facial variation — real consumption can exceed the nominal-joint calculation
- •Grout selection must match the joint width achieved on the wall, not the nominal spec
ANSI A108.10 — Installation of Grout in Tilework(ANSI A108.10)
View StandardThe standard for grouting tile. Requires joints be packed full and uniform, which is the basis for treating joint depth as equal to tile thickness in the coverage formula.
Key Requirements:
- •§5.3.4: all joints filled uniformly and to full depth
- •Cushion- / bevel-edge tile finished to the depth of the cushion (the 1/16" minimum is measured at the base of the bevel)
- •Grout tooled and struck flush; voids and pinholes corrected before cure
- •Excess grout and haze cleaned before set; no skinning over of joints
- •Joint depth = tile thickness for full-fill installations (the calculator's Jd input)
ANSI A118.6 — Standard Cement Grouts(ANSI A118.6)
View StandardDefines standard sanded and unsanded cementitious grouts and the joint widths each is rated for — the sanded-vs-unsanded selection rule.
Key Requirements:
- •Sanded grout for joints wider than 1/8" (3.17 mm) — sand resists shrinkage cracking
- •Unsanded grout for joints 1/8" and narrower
- •Unsanded required on polished/soft stone and glass where sand would scratch the surface
- •Compressive-strength and water-absorption test criteria
- •Color uniformity within a single dye lot
ANSI A118.7 — High-Performance Polymer-Modified Cement Grouts(ANSI A118.7)
View StandardCovers the polymer-modified cementitious grouts most installers actually use — Polyblend Plus, PermaColor, Ultracolor Plus FA, ARDEX FH. Higher bond, lower absorption, freeze-thaw resistance.
Key Requirements:
- •Polymer modification for improved bond strength and reduced water absorption
- •Freeze-thaw resistance for exterior and wet-area applications
- •Sanded and unsanded variants within the same product family
- •Coverage charts published per 10 lb and 25 lb unit
- •Reduced efflorescence vs standard A118.6 grout
ANSI A118.3 — Chemical-Resistant, Water-Cleanable Epoxy Grout(ANSI A118.3)
View StandardThe epoxy grout standard (SPECTRALOCK, Kerapoxy, CEG). Stain- and chemical-resistant, never needs sealing, sold by unit volume rather than weight — handled separately in the calculator.
Key Requirements:
- •Chemical and stain resistance for commercial, wet, and food-prep areas
- •Water-cleanable during the working window
- •Sold by kit/unit (Mini / Full / Commercial) — Full Unit ≈ 188.9 in³ yield
- •No sealing required — inherently non-porous
- •Joint range typically 1/16"–1/2" depending on product
ANSI A108.22 — Installation of Pre-Mixed Grout(ANSI A108.22)
View StandardGoverns single-component, ready-to-use urethane and acrylic grouts (Bostik TruColor, MAPEI Flexcolor CQ). Sold by pail; manufacturers publish coverage directly because density is not standardized.
Key Requirements:
- •Ready-to-use — no field mixing of powder and water
- •Sold by pail volume; use the manufacturer coverage chart directly
- •No sealing required
- •Product-specific joint ranges (e.g. TruColor RapidCure floors 1/16"–1/2", walls 1/16"–1/4")
- •Color consistency without dye-lot variation
ANSI A137.1 — Tile Dimensional Standards(ANSI A137.1)
View StandardDefines rectified vs calibrated tile, facial-dimension variation ranges, warpage, and lippage — the tile-side inputs that set the minimum joint width under A108.02.
Key Requirements:
- •Rectified tile: tightest facial-dimension tolerance, allows minimum joints (1/8" on large format)
- •Calibrated (pressed) tile: wider tolerance, requires larger minimum joints (3/16")
- •Facial-variation classes drive the 3× minimum-joint rule
- •Warpage and wedging limits affecting lippage and joint consistency
- •Nominal vs actual size definitions used by coverage charts
TCNA Handbook — Grout Selection & Movement Joints(TCNA Handbook / EJ171)
View StandardThe Tile Council of North America Handbook is the field reference for grout-type-by-joint-width selection and movement-joint (EJ171) placement. Corners and changes of plane are caulked, not grouted.
Key Requirements:
- •Grout-type selection guide by joint width and tile type
- •EJ171 movement joints: every 8–12 ft interior, 8 ft exterior, at all changes of plane
- •Soft-joint sealant (caulk) at inside corners and wall-to-floor — never rigid grout
- •Coverage charts characterized as estimates 'for estimating purposes'
- •Sealing recommendations for cementitious grout in wet areas
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.
Wet Areas — Showers, Tub Surrounds, and Floors
Quantity unchanged; product and sealing change
Any cementitious grout works in a wet area but must be sealed and periodically re-sealed; epoxy and pre-mixed urethane are preferred for hygiene because they never need sealing. The grout volume is identical — only the product (and its density) shifts.
Regional Examples:
Freeze-Thaw Exteriors
Polymer-modified, freeze-thaw-rated grout and impervious tile
Exterior tile in freezing climates requires freeze-thaw-resistant polymer-modified grout (A118.7) and impervious/vitreous tile, with full, compacted joints and movement joints per TCNA EJ171. Polymer-modified grout absorbs less water, so it survives freeze cycles.
Regional Examples:
Large-Format vs Mosaic — The Coverage Swing
The perimeter-to-area ratio causes a > 10× swing in coverage
Because grout scales with the perimeter-to-area ratio, a single 25-lb bag covers roughly 54 sq ft of 1×1 mosaic but 348–688 sq ft of 12×12 to 24×24 tile. The calculator MUST use the individual tile dimension for mosaics, not the mesh-sheet size, or it will underestimate by an order of magnitude.
Regional Examples:
Natural Stone & Polished Surfaces
Sanded grout scratches — switch to unsanded or fine-aggregate
Polished marble, limestone, travertine, and other soft or polished stone scratch under sanded grout. Use unsanded or a fine-aggregate grout. This changes product selection and density slightly, not the joint geometry.
Regional Examples:
Porous & Unglazed Tile — Waste and Sealing
Add 12–15% waste; seal the tile before grouting
Unglazed quarry tile, terracotta, slate, and cement tile absorb grout during cleanup and stain easily. Laticrete's charts call for an extra 10–15% on unglazed quarry tile, and the tile should be sealed before grouting to prevent grout haze.
Regional Examples:
Tile Thickness by Type — The Joint-Depth Input
Thickness sets joint depth and drives volume linearly
Joint depth equals tile thickness for full-fill installations, and thickness varies widely by tile type — from 1/8" glass mosaic to 5/8" cement tile. Getting the thickness input right matters as much as the joint width, since grout scales linearly with both.
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
Share this calculator with your customers
Run a contractor site, supply store, or blog? Drop this free grout calculator straight onto your own page so your visitors can estimate materials without leaving. No signup, works on any website — just copy and paste.
Small project — do you need a dumpster at all?
Projects this size often fit in a Bagster (up to 3 cubic yards). See how Bagster bags compare to a 10-yard dumpster on cost, access, and material limits.
Compare Bagster vs. Dumpster →
Related Calculators
Tile Calculator
Calculate tiles, thin-set, grout (TCNA formula), membrane, leveling clips & EJ171 movement joints for floor, wall or shower. Free, no signup.
Backsplash Tile Calculator
Instantly calculate backsplash tiles, grout bags, thinset & trim for ceramic, glass, marble & mosaic. TCNA/ANSI formulas. Free, no signup needed.
Mortar / Thinset Calculator
Pick the right ANSI mortar (A118.1/.4/.11/.15/.3 or A136.1 mastic) for substrate and tile, then get bag count by trowel notch. NTCA, TCNA, ANSI A108.
Floor Mud Calculator
Free floor mud / deck mud calculator. Bag count, mortar bed volume & cement-sand ratios for shower pans, pre-slope & flat floors per ANSI A108.1A.
How to Use This Calculator
- Pick a tile preset (mosaic, subway, 12×12, large format, plank) to auto-fill dimensions — or choose Custom and enter your own.
- Enter or confirm tile length, width, and thickness in inches. For mosaics, use the individual tile (chip) size, NOT the mesh-sheet size — this is the single biggest estimating mistake.
- Pick your grout joint width (1/16" to 1/2"). The minimum is 1/16" and at least 3× the tile's facial-dimension variation per ANSI A108.02.
- Enter the tiled area in square feet. Not sure? Run the Tile or Flooring calculator first, then bring the area back here.
- Choose the grout type: unsanded (1/16"–1/8" joints, polished stone/glass), sanded (1/8"–1/2" joints), or epoxy (wet/commercial, sold by kit). The calculator flags a type that conflicts with your joint width.
- Pick a waste factor: 5% clean pro straight-lay, 10% standard (recommended), or 12–20% for porous/unglazed tile, mosaics, and complex layouts.
- Click Calculate: see coverage (in³ per sq ft), total grout needed in pounds, the bags and boxes to buy (or epoxy Full Units), the full calculation breakdown, and installation notes.
How the Grout Coverage Math Works
Grout quantity is geometry. The amount per square foot equals the joint length per square foot times the joint cross-section: [(L+W)/(L×W)] × Jw × Jd, multiplied by 144 to convert to cubic inches per square foot. The term (L+W)/(L×W) is the tile's perimeter-to-area ratio — it is why a 1×1 mosaic uses about 12× the grout of a 12×12 tile at the same joint. To convert volume to weight, divide by 1728 (in³ per ft³) and multiply by grout density (≈100–110 lb/ft³, back-calculated from manufacturer charts). The full formula is Grout(lbs) = [(L+W)/(L×W)] × Jw × Jd × Area × K, where K = (144/1728) × density ≈ 8.25 (Laticrete/MAPEI) to 9.2 (Custom Building Products). We default to the conservative high end so the tool never under-buys, then round up to whole bags or boxes. Epoxy is handled by volume: total joint cubic inches ÷ 188.9 in³ per Full Unit, rounded up.
Frequently Asked Questions
How much grout do I need for 100 sq ft of 12×12 tile?
For 12×12 tile that's 3/8" thick with a 1/8" joint, 100 sq ft needs about 6.5–7.2 lb of cementitious grout — roughly 7.2–7.9 lb with 10% waste, which is one small box (or one 25-lb bag with plenty to spare). Manufacturer coverage charts confirm this: a single 25-lb bag covers 348 sq ft (Custom Building Products) to 388 sq ft (Laticrete/MAPEI) of this exact tile and joint. The calculator computes 1.125 in³ of grout per square foot for this combination.
Should I use sanded or unsanded grout?
Use unsanded grout for joints 1/16"–1/8" wide, and for polished or soft stone (marble, limestone) and glass tile where sand would scratch the surface. Use sanded grout for joints 1/8"–1/2" — the sand resists the shrinkage cracking that unsanded grout suffers in wider joints. Per ANSI A118.6, sanded is specifically for joints wider than 1/8". The calculator auto-checks your selected type against your joint width and warns you if they conflict. The grout type diagram matches joint width to grout type.
Why does grout coverage change so much with tile size?
Because smaller tiles pack far more linear feet of grout joint into each square foot. Coverage scales with the perimeter-to-area ratio (L+W)/(L×W): a 1×1 mosaic has a ratio of 2.0 per inch while a 12×12 tile has only 0.167 per inch — 12× more joint length per square foot. That's why one 25-lb bag covers only ~54 sq ft of 1×1 mosaic but over 340 sq ft of 12×12 tile at the same joint width. A 3×6 subway tile uses nearly 2× the grout of a 12×12 per square foot even though it's thinner. The grout coverage diagram shows why small tile needs more grout.
Do wider grout joints use more grout?
Yes — grout scales linearly with both joint width and joint depth (tile thickness). Doubling the joint from 1/8" to 1/4" roughly doubles the grout; going from 1/8" to 3/8" roughly triples it. Joint width is often the single biggest variable in the estimate, which is why this calculator asks for it explicitly rather than assuming a default. Joint depth matters just as much: a shortcut formula that ignores tile thickness can be 40% short on thick floor tile or 80% over on thin mosaics. The grout joint diagram shows the joint as a width × depth channel.
What waste factor should I add for grout?
10% is the standard default (MAPEI/Laticrete/NTCA consensus) — it covers mixing and bucket loss, sponge cleanup, partial-bag rounding, and joint-width variation. Drop to 5% for clean straight-lay work by professionals; bump to 12–15% for porous or unglazed quarry tile (which absorbs grout during cleanup) and for mosaics; up to 20% for diagonal, herringbone, or complex layouts. Always buy from one dye lot and keep a reserve bag from the same lot for touch-ups, since re-orders rarely match exactly.
How is epoxy grout estimated differently?
Epoxy grout (ANSI A118.3, e.g. Laticrete SPECTRALOCK, MAPEI Kerapoxy) is sold by kit volume, not by the pound, so the calculator switches to a volume pipeline: it computes your total joint volume in cubic inches, adds waste, then divides by the Full-Unit yield (188.9 in³ for SPECTRALOCK) and rounds up to whole units. One Full Unit equals four Mini Units, so small jobs often fit a single Mini Unit. Epoxy is stain- and chemical-resistant and never needs sealing — the best choice for showers, commercial floors, and food-prep areas.
Do I need to seal grout, and does this calculator include sealer?
Cementitious grout (sanded and unsanded) should be sealed after it cures and re-sealed every 1–3 years in wet areas to resist staining and moisture. Epoxy and pre-mixed urethane grouts are inherently stain- and moisture-resistant and never need sealing. This calculator outputs grout quantity only — it does not calculate sealer, thinset/mortar, or caulk. Use the Mortar / Thinset calculator for setting material, and caulk inside corners and changes of plane rather than grouting them (TCNA EJ171).