How to use the grout calculator
- Enter the area you are grouting.
- Enter the tile length, width and thickness in inches. Thickness sets how deep the joints are.
- Choose the joint width. The table shows how much more grout wider joints take.
- Pick a bag size under Adjust assumptions.
The grout formula
Cubic inches per sq ft = 144 × (L + W) × joint × depth ÷ (L × W)
Pounds = cubic inches × 0.06 lb × area × (1 + extra)
L and W are the tile length and width, all in inches.
Worked example
A 30 sq ft backsplash of 3 × 6 in subway tile, 5/16 in thick, 1/16 in joints
- 144 × (3 + 6) × 0.0625 × 0.3125 ÷ (3 × 6) = 1.41 cubic inches per sq ft.
- × 0.06 lb = 0.084 lb per sq ft; × 30 sq ft × 1.10 = 2.8 lb of grout.
- One 7 or 10 lb bag is plenty.
Why small tiles use more grout
Grout fills the joints around every tile. Halve the tile size and you roughly double the length of joints per square foot. Mosaics use several times more grout than large-format tile for the same area.
| Tile (3/8 in thick) | 1/16 in joint | 1/8 in joint | 1/4 in joint |
|---|---|---|---|
| 2 × 2 in mosaic | 20.3 lb | 40.5 lb | 81 lb |
| 3 × 6 in subway | 10.1 lb | 20.3 lb | 40.5 lb |
| 6 × 6 in | 6.8 lb | 13.5 lb | 27 lb |
| 12 × 12 in | 3.4 lb | 6.8 lb | 13.5 lb |
| 12 × 24 in | 2.5 lb | 5.1 lb | 10.1 lb |
Pounds per 100 sq ft, before extra.
Common mistakes to avoid
- Ignoring tile thickness. Thick tile has deep joints that take more grout.
- Sanded grout in tiny joints. Joints under 1/8 in need unsanded grout.
- Mixing too much. Grout stiffens; mix small batches.
- Different batches, different colors. Mix all bags the same way with the same water.
Frequently asked questions
How do I calculate grout?
Grout volume per square foot = 144 × (tile length + tile width) × joint width × tile thickness ÷ (tile length × tile width), in inches. Multiply by about 0.06 lb per cubic inch for cement grout and by the area.
How much grout for a backsplash?
A 30 sq ft backsplash of 3 × 6 in subway tile, 5/16 in thick with 1/16 in joints, uses about 2.8 lb of grout including 10% extra: one small bag.
How much grout for 100 sq ft of 12 × 12 tile?
With 1/8 in joints and 3/8 in thick tile, about 6.75 lb (7.4 lb with 10% extra). With 1/4 in joints it doubles.
Sanded or unsanded grout?
Unsanded for joints narrower than 1/8 in, especially on polished stone and glass that sand can scratch. Sanded for joints 1/8 in and wider, where it resists cracking and shrinking.
Why does my grout bag cover less than the chart?
Joint depth matters: thick tiles have deeper joints. Waste in the bucket, cleanup and slightly wider joints also add up. We add 10% by default.