How this calculator works
Grout fills the joints between tiles, so the amount depends on how many feet of joint there are per square foot (smaller tiles mean more joints), how wide the joints are and how deep — the tile thickness. Per square foot, the joint length is 144 × (L + W) ÷ (L × W) inches; multiply by joint width and tile thickness to get cubic inches.
One pound of mixed sanded grout fills about 15.8 cubic inches. That figure is calibrated to Custom Building Products’ Polyblend Plus coverage chart, where a 25 lb bag covers about 348 sq ft of 12 × 12 × 3/8 in tile with 1/8 in joints.
Assumptions and tips
- Joints filled to the full tile thickness. Natural stone, uneven or pillowed edges and textured tile use more.
- Epoxy and urethane grouts have different yields — check the product chart.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Tiled area | 100 sq ft |
| Tile length | 12 in |
| Tile width | 12 in |
| Tile thickness | 0.375 in |
| Grout joint width | 0.125 in |
| Waste allowance | 10 % |
| Bag size | 25 lb bag |
| Result | Value |
|---|---|
| Grout needed | 7.8 lb |
| 25 lb bags | 1 bags |
| Coverage per 25 lb bag | 351 sq ft |
| Joint volume | 124 cu in |
| Grout type | Sanded (joints 1/8 in and wider) |
Step by step:
- Joint per sq ft = 144 × (12 + 12) ÷ (12 × 12) = 24 in of joint
- × 0.125 in wide × 0.375 in deep = 1.125 cu in per sq ft
- × 100 sq ft × 1.1 waste = 123.8 cu in
- 123.8 ÷ 15.8 cu in per lb = 7.8 lb
Grout for 100 sq ft (1/8 in joints, 10% waste)
Calculated with this tool for common tile sizes.
| Tile | Grout needed | Coverage per 25 lb bag |
|---|---|---|
| 2 × 2 in | 31.3 lb | 88 sq ft |
| 3 × 6 in | 19.6 lb | 140 sq ft |
| 4 × 4 in | 15.7 lb | 176 sq ft |
| 6 × 6 in | 13.1 lb | 211 sq ft |
| 12 × 12 in | 7.8 lb | 351 sq ft |
| 12 × 24 in | 5.9 lb | 468 sq ft |
| 18 × 18 in | 5.2 lb | 527 sq ft |
| 24 × 24 in | 3.9 lb | 702 sq ft |
| 6 × 36 in | 9.1 lb | 301 sq ft |
Common mistakes to avoid
- Buying by area alone — 1 × 1 mosaics use about six times the grout of 12 × 12 tile.
- Mixing the whole bag at once; mix only what you can use in about 30 minutes.
Frequently asked questions
How much grout for 100 sq ft of 12 × 12 tile?
With 1/8 in joints and 3/8 in tile, about 7.8 lb with 10% waste — one 25 lb bag is plenty.
How far does a 25 lb bag of grout go?
From about 54 sq ft (1 × 1 mosaic, 1/8 in joints) to almost 700 sq ft (24 × 24 tile, 1/8 in joints).
Sanded or unsanded grout?
Use sanded grout for joints 1/8 in and wider, unsanded for narrower joints and for easily scratched surfaces like polished marble.
Sources
Built and reviewed by Anirban Kundu, Creator & Editor · M.Sc Physics, 20 years teaching science