About the grout calculator
Grout fills the joints between tiles, so the amount you need depends on how much joint there is: small tiles and wide, deep joints use a lot more grout than large tiles with narrow joints. This calculator uses the standard joint-volume formula and converts it to weight with an editable density, so you can match your product.
Grout manufacturers publish their own coverage charts. When your product has one, use it to double-check this estimate.
How to use it
- Enter the tiled area.
- Enter the tile length, width and thickness. Thickness is used as the joint depth.
- Enter the joint width (fractions such as 1/16 or 1/8 are fine).
- Adjust the density if your product data sheet gives one, and enter the bag size.
Formula
Joint length per unit area
j = (L + W) ÷ (L × W)Grout volume
V = area × j × joint width × joint depth × (1 + waste %)Grout weight
M = V × density- The default density of ≈1.6 kg/L (≈100 lb/ft³) is a typical figure for cement-based grout; epoxy and other grouts differ.
Worked example: 100 ft² of 12 × 12 in tile, 3/8 in thick, 1/8 in joints
- Joint length = (1 + 1) ÷ (1 × 1) = 2 ft per ft² → 200 ft = 2,400 in
- Volume = 2,400 × 0.125 × 0.375 = 112.5 in³
- +10 % = 123.75 in³ ≈ 0.072 ft³
- Weight ≈ 0.072 × 100 = 7.2 lb
Result: About 7 lb of grout — one 10 lb or 25 lb bag.
Assumptions and limitations
- Joints are assumed to be filled to the full tile thickness.
- Mosaic sheets with very small tiles may need much more grout than larger tiles of the same area.
Frequently asked questions
How much grout do I need per square foot?
It depends on tile size and joint width. For 12 × 12 in tile with 1/8 in joints and 3/8 in thickness, about 0.07 lb per ft². Small mosaics can need many times more.
Sanded or unsanded grout?
That depends on joint width and tile type; follow the grout and tile manufacturers' recommendations. The quantity calculation is the same.
Why is my result different from the bag's coverage chart?
Charts use the manufacturer's own density and assumptions. If they differ, trust the chart for that product.
Sources and further reading
Results are estimates for planning purposes. See our disclaimer for details.