How Much Grout Do I Need?
The most mis-estimated material in tiling. Smaller tiles need dramatically more grout.
100 square feet of 12×12 tile with 1/4-inch joints needs about 21 lb of grout — three 10 lb bags. Change the tile to 2×2 mosaic with the same joints and the same area needs over 120 lb. That is a six-fold difference for the same floor.
Estimates only. Textured walls, high ceilings, sprayers and major colour changes can all increase the amount you need. Always buy slightly more than the calculation suggests.
Grout needed for 100 sq ft, by tile size
| Area | Surface | Tile size | Tiles | Boxes | Tile cost |
|---|---|---|---|---|---|
| 24x24 large format | 100 sq ft | 24" × 24" | 28 | 3 boxes | $105 |
| 12x24 plank | 100 sq ft | 12" × 24" | 55 | 6 boxes | $210 |
| 12x12 standard | 100 sq ft | 12" × 12" | 110 | 11 boxes | $385 |
| 6x6 | 100 sq ft | 6" × 6" | 440 | 44 boxes | $1,540 |
| 3x6 subway | 100 sq ft | 3" × 6" | 880 | 88 boxes | $3,080 |
| 2x2 mosaic | 100 sq ft | 2" × 2" | 3,960 | 396 boxes | $13,860 |
All at 1/4-inch joints and 3/8-inch tile thickness, so only the tile size changes. This is the comparison that shows why small tiles need so much more grout.
What actually determines grout use
Grout fills the gaps between tiles, so what matters is the total volume of the joints. Three things drive it:
- Tile size. This is the big one, and it works opposite to intuition. Halve the tile size and you get four times as many tiles, which means roughly four times as much joint length per square foot.
- Joint width. Doubling the joint width doubles the grout, exactly.
- Tile thickness. A thicker tile means a deeper joint. Doubling the thickness doubles the grout.
This calculator works from the joint volume rather than a lookup table, so it stays accurate for any combination you throw at it — including the awkward ones like 3×12 planks or hexagon mosaics.
Why you must never guess grout
There is a second reason to get this right beyond the cost. Grout must come from a single batch.
If you run out halfway through and buy more, the colour will not match. Cementitious grout is mixed from pigments that vary between production runs, and the difference shows on a floor in normal daylight.
Grout is also cheap relative to the labour you have already invested. Buying an extra bag costs a few dollars. Running out at 80 % complete, with a floor that has to be cleaned and re-grouted in two colours, costs a day.
Sanded or unsanded?
The choice is decided by the joint width, not by preference:
- Unsanded grout for joints under 1/8 inch. Sand grains cannot fit into a narrow joint, and forcing them in scratches polished tile.
- Sanded grout for joints of 1/8 inch and wider. The sand gives the grout strength and stops it shrinking and cracking as it dries.
For very wide joints, or for a shower, epoxy grout is worth the cost: it does not need sealing and resists staining far better than cementitious grout.
Frequently asked questions
How much grout do I need for 100 sq ft of tile?
About 21 lb for 12x12 tile with 1/4-inch joints and 3/8-inch thickness. The same area in 2x2 mosaic with the same joints needs over 120 lb.
Why do small tiles need more grout?
Because grout fills joints. Smaller tiles mean more tiles per square foot, which means more joint length, which means more grout volume. Halving the tile size roughly quadruples the grout.
Does tile thickness affect grout?
Yes. Grout fills the full depth of the joint, so a thicker tile means a deeper joint and proportionally more grout.
Should I use sanded or unsanded grout?
Unsanded for joints under 1/8 inch, sanded for 1/8 inch and wider. Sanded grout is stronger and resists cracking, but scratches polished tile in narrow joints.