How much grout do I need?
Grout fills the joints between tiles. The amount depends on the total length of joints per square foot, which is set by the tile size, and on the joint’s width and depth.
Joint volume per area = (L + W) ÷ (L × W) × joint width × joint depth
with L and W the tile length and width. Multiply by the grout’s density (about 1.6 kg per liter for cement grout) to get the weight, then add a waste allowance.
Example
12 × 12 in tiles, 1/8 in joints, 3/8 in deep, 100 ft²:
- joint volume: (12 + 12) ÷ 144 × 0.125 × 0.375 × 144 ≈ 1.1 cubic inches per ft², or about 1.8 liters in total;
- grout weight: about 6.5 lb, or 7.2 lb with 10% waste;
- one 25 lb bag is plenty.
What changes the quantity
- Smaller tiles mean many more joints: 2 × 2 in mosaics need about six times as much grout as 12 × 12 in tiles for the same joint size.
- Wider joints increase grout linearly: a 1/4 in joint takes twice as much as a 1/8 in joint.
- Thicker tiles have deeper joints and need proportionally more grout.
- Rough or irregular tiles, such as handmade or natural stone, often need 20% or more extra.
Sanded or unsanded?
- Unsanded grout suits joints narrower than 1/8 in and polished stone that sand could scratch.
- Sanded grout is stronger and shrinks less in joints of 1/8 in and wider.
- Epoxy grout resists stains and water best, which makes it a good choice for showers and kitchens, but it is harder to work and more expensive. Its density is a little lower.
Tips
- Wait for the thinset to cure, usually 24 hours, before grouting.
- Mix only what you can use in about 30 minutes.
- Work diagonally across the joints with a rubber float, then clean with a damp sponge once the grout firms up.
- Seal cement grout after it cures, typically after 48 to 72 hours, to resist stains.
- Use flexible caulk, not grout, at inside corners and where tile meets a tub or other material.