Tile Grout Quantity Calculator
Grout fills the joints between tiles, and the amount you need depends on tile size, joint width, joint depth, and the area being tiled. Smaller tiles and wider, deeper joints use far more grout per square foot. This calculator uses the widely used grout coverage formula to estimate the volume of joint space and convert it to an approximate weight of dry grout, with a waste allowance.
Grout quantity formula
Joint volume per sq ft = 144 * ((tile L + tile W) / (tile L * tile W)) * joint width * joint depth
(all lengths in inches, result is cubic inches per square foot)
Grout volume (cu ft) = joint volume per sq ft * area / 1,728
Grout weight (lb) = grout volume * density
With waste = grout weight * (1 + waste / 100)
The factor (L + W) / (L * W) captures how much joint length exists per tile face area: smaller tiles have proportionally more joint. There are 1,728 cubic inches in a cubic foot. Dry grout density is typically around 100 to 125 lb per cubic foot.
Worked example
For 12 by 12 inch tiles with a 1/8 inch (0.125) joint, 3/8 inch (0.375) deep, over 100 square feet: joint volume per square foot = 144 times ((12 + 12) / (12 times 12)) times 0.125 times 0.375 = 1.125 cubic inches. Total joint volume = 1.125 times 100 = 112.5 cubic inches = 0.065 cubic feet. At 115 lb per cubic foot that is about 7.49 lb of grout. Large tiles use very little grout; small mosaic tiles would need many times more for the same area.
Grout estimating notes
- Smaller tiles mean more total joint length per square foot, so they consume more grout.
- Wider and deeper joints increase grout use proportionally.
- Dry grout density varies by product, roughly 100 to 125 lb per cubic foot; check the bag.
- Always add a waste allowance (typically 10 percent) for mixing losses and partial bags.
- Manufacturer coverage charts are the authoritative reference for a specific grout product.
Tile Grout Quantity Calculator: frequently asked questions
How much grout do I need per square foot?
It depends on tile size and joint dimensions. Larger tiles with thin joints may use under half a pound per square foot, while small mosaic tiles with wide joints can use several times that. This calculator computes the exact amount from your inputs.
Why do smaller tiles need more grout?
Smaller tiles have more total joint length within a given area, because there are more tile edges per square foot. More joint length means more grout volume, so a mosaic uses much more grout than a large-format tile over the same area.
What is grout joint depth?
Joint depth is how deep the grout fills between tiles, usually equal to the tile thickness. A thicker tile creates a deeper joint, which uses more grout per linear foot of joint.
Should I buy extra grout?
Yes. Add at least a 10 percent waste allowance for mixing losses, spillage, and the practical reality that grout comes in fixed bag sizes. This calculator includes an editable waste percentage.
Sources and methodology
- The grout-joint volume formula ((L + W) / (L * W) times joint width times depth) is a standard tiling geometry derivation; 1,728 cubic inches per cubic foot is a fixed unit conversion.
- Grout density and waste are user-editable inputs; consult the manufacturer coverage chart for a specific product.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.