The amount of grout you need depends on four things: the area you're tiling, the tile size, the joint width, and the tile thickness. Tile size matters most. Small tiles have many more joints per square foot, so a mosaic can need several times more grout than large floor tile.
Skip the math: use the grout calculator →
Grout coverage chart
Estimates for 100 square feet of tile. Scale up or down for your area. For example, 50 sq ft needs half the amount shown.
| Tile | Thickness | Joint | Sanded | Unsanded |
|---|---|---|---|---|
| 2×2" mosaic | 1/4" | 1/8" | 27.3 lbs | 22.4 lbs |
| 3×6" subway | 5/16" | 1/16" | 8.5 lbs | 7.0 lbs |
| 4×4" | 1/4" | 1/8" | 13.6 lbs | 11.2 lbs |
| 6×6" | 3/8" | 1/8" | 13.6 lbs | 11.2 lbs |
| 12×12" | 3/8" | 1/8" | 6.8 lbs | 5.6 lbs |
| 12×24" | 3/8" | 1/8" | 5.1 lbs | 4.2 lbs |
| 18×18" | 3/8" | 3/16" | 6.8 lbs | 5.6 lbs |
| 24×24" | 3/8" | 1/8" | 3.4 lbs | 2.8 lbs |
The grout formula
Grout fills the joints between tiles, so the amount you need is the volume of those joints:
volume = total joint length × joint width × joint depth
The joint depth is the tile thickness. To find the total joint length, count how many tiles cover the area and multiply by the joint length each tile adds. Neighboring tiles share a joint, so each rectangular tile adds one length plus one width (not all four sides). Finally, convert volume to weight using the grout's density, since grout is sold by the pound.
Worked example: 100 sq ft of 12×12 tile
Tile is 12×12", 3/8" thick, with 1/8" joints.
- Area in square inches: 100 sq ft × 144 = 14,400 sq in.
- Number of tiles: 14,400 ÷ (12 × 12) = 100 tiles.
- Joint length: each tile adds 12 + 12 = 24", so 100 × 24 = 2,400".
- Volume: 2,400 × 0.125 × 0.375 = 112.5 cubic inches.
- Weight: sanded grout weighs about 0.061 lbs per cubic inch (~104 lbs per cubic foot), so 112.5 × 0.0606 ≈ 6.8 lbs.
- Add overage: with 10% extra, buy about 7.5 lbs. A single 10 lb bag covers it.
Why buy extra grout?
Some grout is always lost: it's left in the bucket, wiped off during cleanup, or mixed in a batch that sets before you use it. Buying 10–15% extra covers that waste and leaves a little for future repairs. Grout color can vary slightly between production batches, so it's safer to buy everything at once than to run out mid-job.
Converting pounds to bags
Grout is commonly sold in bags of around 10 and 25 lbs. Divide your total by the bag size and round up. Many manufacturers also print a coverage chart on the bag. If it differs from your estimate, go with the higher number.
What this formula doesn't cover
- The formula assumes joints are filled to the full thickness of the tile. In practice, thinset fills part of the joint, so the estimate leans toward having enough.
- Penny round tile leaves gaps between circles that aren't straight joints, so the calculator uses a different formula for it. See the penny tile grout calculator.
- Pre-mixed and epoxy grouts are often sold by volume rather than weight. Check the product's own coverage chart.
Not sure which type to buy? See sanded vs. unsanded grout.