Grout Calculator
Estimate how many pounds of tile grout you need from the tile size, joint width and the area you are tiling.
How it works
grout per ft² = ((tileL + tileW) ÷ (tileL × tileW)) × joint width × tile thickness × 12.5 · total = per ft² × area, then + 10%
Grout fills the joints between tiles, so the amount depends on how much joint there is per square foot — which rises as tiles get smaller (more joints) and as joints get wider or tiles thicker. The coverage factor combines the joint volume per unit area with a density constant to give pounds per square foot; multiplying by your area and adding 10% for waste, mixing loss and partial bags gives the pounds to buy. All tile dimensions are in inches.
Worked example
For 100 ft² of 12 × 12 in tile, 3/8 in thick, with 1/8 in joints: ((12 + 12) ÷ 144) × 0.125 × 0.375 × 12.5 ≈ 0.098 lb/ft². Over 100 ft² that is about 9.8 lb, or roughly 10.7 lb with 10% waste — about one standard bag.
Frequently asked questions
Sanded or unsanded grout?
Use sanded grout for joints 1/8 in and wider — the sand resists shrinkage and cracking. Unsanded grout is for narrow joints under 1/8 in and for polished or soft stone that sand would scratch. This estimate is by weight and applies to either.
Why do smaller tiles need more grout?
More, smaller tiles pack more linear inches of joint into each square foot. A mosaic sheet has far more joint per area than a large-format tile, so it can use several times the grout for the same floor.
Should I round up to whole bags?
Yes. Grout is sold in fixed bag sizes (often 10 or 25 lb), and mixing a second partial batch to a matching color and consistency is hard. Buy the next whole bag and keep the remainder sealed for repairs.
Related calculators
Estimate for planning. Add a waste margin and confirm with your supplier and local codes.