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
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"+.
Joint & area
Minimum joint is 1/16" and at least 3× the tile's facial-dimension variation (ANSI A108.02 §4.3.8). Not sure of your area? Run the Tile or Flooring calculator first.
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).
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 →
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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.
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.
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.
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).