How much grout do I need?
Grout use depends on four things: tile length, tile width, joint width and tile thickness. Big tiles with thin joints use very little; small mosaic with wide joints can use ten times as much per square foot.
For 12 × 24 in tile at 3/8 in thick with 1/8 in joints, the joints are about 1.5% of the surface, which works out at 0.05 lb per square foot. A 25 lb bag covers roughly 500 square feet in theory — call it 415 once you allow for what never leaves the bucket.
The same 1/8 in joint on 2 × 2 in mosaic is over 11% of the surface — seven times as much grout per square foot. That 25 lb bag now covers about 56 square feet. If you scale from a job you did last year without checking the tile size, you will be badly wrong in one direction or the other.
How the calculation works
The joint fraction is 1 − (tile area ÷ module area), where the module is the tile plus one joint on each dimension. For a 12 × 12 tile with a 1/8 in joint that is 1 − (144 ÷ 146.5) = 1.7% of the surface.
Multiply that fraction by 144 square inches and by the tile thickness to get cubic inches of grout per square foot, then by about 0.06 lb per cubic inch — dry cement grout runs roughly 103 lb per cubic foot.
Depth matters as much as width and gets ignored constantly. The joint is as deep as the tile is thick, so 1/2 in porcelain needs a third more grout than 3/8 in for the identical layout.
Manufacturer coverage charts are theoretical. Real use runs 15–25% higher because grout stays in the bucket, on the float, and in every rinse of the sponge. The default 20% allowance here reflects what actually leaves the bag.
Typical grout cost, mid-2026
| Material | Unit | Typical range |
|---|---|---|
| Sanded cement grout, 25 lb | per bag | $18.00 – $32.00 |
| Unsanded cement grout, 10 lb | per bag | $14.00 – $26.00 |
| Premium / high-performance grout | per 25 lb | $30.00 – $55.00 |
| Epoxy groutStain-proof, unforgiving to work | per kit | $60.00 – $140 |
| Grout sealer | per quart | $20.00 – $45.00 |
| Grout float and sponges | set | $20.00 – $50.00 |
| Grouting labour | per sq ft | $1.50 – $4.00 |
Epoxy grout costs several times more and does not need sealing. On a kitchen floor or a shower it usually pays for itself; on a 500 sq ft floor it is a hard day for anyone who has not used it before.
What goes wrong on this job
- Dry-blend every bag together before adding water. Colour varies between dye lots by enough to see, and the boundary always lands in the middle of the most visible run.
- Match the grout to the joint, not to the tile. Sanded for 1/8 in and wider, unsanded below — using unsanded in a wide joint gives you shrinkage cracks within weeks.
- Never use sanded grout on polished marble or glass without testing. The sand scratches, and you will not notice until the light comes across the floor in the afternoon.
- Mix to the manufacturer water ratio and let it slake for the stated time, then remix without adding water. Extra water is the single biggest cause of weak, patchy, colour-inconsistent grout.
- Buy 20% more than the chart says and keep the offcut bag. Matching grout a year later for a repair is close to impossible.
Frequently asked questions
How much grout do I need per square foot?
It depends entirely on tile size and joint width. About 0.05 lb per square foot for 12 × 24 in tile with 1/8 in joints, but 0.37 lb per square foot for 2 in mosaic with the same joint — seven times as much.
How many square feet does a 25 lb bag of grout cover?
Around 415 sq ft for 12 × 24 in tile at 3/8 in thick with 1/8 in joints, about 310 sq ft for 12 × 12 in, and only 56 sq ft for 2 in mosaic. Always check against your actual tile size.
Should I use sanded or unsanded grout?
Sanded for joints 1/8 in and wider, unsanded for anything narrower. Unsanded shrinks and cracks in wide joints; sanded will not pack into narrow ones and can scratch polished surfaces.
Why did I run out of grout when the bag said it would cover the floor?
Coverage charts are theoretical and ignore what stays in the bucket, on the float and in the sponge water — typically 15–25% of the bag. They also assume your exact tile size and joint width.