100 square feet of 12 × 12 in tile ⅜ in thick with 3/16 in joints takes about 10.4 lb of cement grout — 11.4 lb with 10 % for losses, less than half of a 25 lb bag of sanded grout. Grout depends less on the area than on the joints: the same floor in 6 × 6 in tile takes twice as much. The calculator above works it out from the tile size, the joint width and the tile thickness.
How the calculator works
Enter the area to grout — directly, or as a floor or walls — the tile length, width and thickness, and the joint width. Choose cement or epoxy grout and the bag size. The result is the grout in pounds and bags, sanded or unsanded, along with the tiles, thinset and boxes for the same surface.
The formula
Every square foot of tiled surface holds (L + W) ÷ (L × W) of joint length per unit of area; each joint is as wide as the joint and as deep as the tile. Multiply by the density of the grout — about 1.7 g/cm³ for cement grout, 1.5 for epoxy — and you have the grout per area.
| Tile, ⅜ in thick | Joint | Grout per 100 ft² |
|---|---|---|
| 6 × 6 in | ⅛ in | 13.8 lb |
| 12 × 12 in | 3/16 in | 10.4 lb |
| 12 × 24 in | ⅛ in | 5.2 lb |
| 24 × 24 in | 3/16 in | 5.2 lb |
Sanded or unsanded
Joints wider than ⅛ in take sanded grout: the sand keeps it from shrinking and cracking. Joints of ⅛ in and less take unsanded grout, which also suits polished marble and glass tile that sand would scratch (ANSI A108.10). Epoxy grout resists stains and needs no sealing, but sets fast — mix small batches.
Common mistakes
- Grout by area alone. Tile size and joint width change it fourfold.
- Forgetting the tile thickness. ½ in tile takes a third more grout than ⅜ in.
- Mixing the whole bag. Cement grout stiffens in 30–60 minutes; mix what you can finish.
For the tiles, thinset and boxes, use the Tile Calculator.