Grout Calculator
Pounds and bags of grout for any tile size and joint width
Grouting a floor, wall or backsplash? Enter your area, tile size, tile thickness and joint width to get the pounds of grout you need and the number of bags to buy. Grout use is driven by joint length per square foot, which is why small tiles can need ten times more grout than large ones over the same floor.
How much grout do I need?
Grout fills the gaps, so the maths is about the joints, not the tile. In a grid of tiles measuring A × B with a joint width C, each repeating cell is (A+C) × (B+C). Subtract the tile face and you have the joint area; multiply by the joint depth (your tile thickness) and you have the volume of grout per cell.
Four things change the answer, and tile size matters most:
- Tile size — smaller tiles mean far more joint length per square foot.
- Joint width — wider joints scale the volume directly.
- Tile thickness — the joint is as deep as the tile, so this scales it too.
- Waste — grout left in the bucket, on the float and in the sponge is a real and large loss.
Rule of thumb: a mosaic sheet can use ten times the grout of a 24 × 24 cm tile over the same floor. Never estimate grout from area alone.
Grout coverage chart by tile size
Grout per square foot is easiest read at scale, so this shows pounds per 100 ft² of floor, before waste, at typical tile thicknesses. Read down your tile size and across to your joint width.
| Tile size | 1/16 in joint | 1/8 in joint | 3/16 in joint | 1/4 in joint |
|---|---|---|---|---|
| 1 × 1 in mosaic | 28.5 lb | 52.5 lb | 72.7 lb | 90.0 lb |
| 4 × 4 in | 9.5 lb | 18.7 lb | 27.4 lb | 35.7 lb |
| 6 × 6 in | 6.4 lb | 12.6 lb | 18.7 lb | 24.5 lb |
| 12 × 12 in | 3.9 lb | 7.7 lb | 11.4 lb | 15.1 lb |
| 12 × 24 in | 2.9 lb | 5.8 lb | 8.6 lb | 11.4 lb |
| 24 × 24 in | 2.3 lb | 4.5 lb | 6.8 lb | 9.0 lb |
Notice that doubling the joint from 1/8 to 1/4 inch roughly doubles the grout, while dropping from 12 × 12 to 4 × 4 tile more than doubles it again.
Why grout coverage charts disagree
If you compare a few manufacturers you will find coverage figures for the same tile that differ by two or three times. That is not an error in any of them, and it is worth understanding before you buy.
The geometry is fixed: a 12 × 12 in tile, 3/8 in thick, with 1/8 in joints needs about 7.7 lb per 100 ft² of grout to fill the joints. Some manufacturer charts agree closely with that. Others quote 15 to 18 lb for the same job, because their figure assumes real-site loss: what stays in the mixing bucket, what the float and sponge take away, and what gets scraped off during cleanup. On a small bathroom that loss can genuinely be half of what you mix.
This calculator gives you the geometric requirement plus your chosen waste percentage, defaulting to 20%. If your bag's own chart is more conservative, trust the bag — and buy one spare either way.
Running out mid-job is the expensive mistake. Grout colour varies between batches and between mixes, so a floor finished from a second bag mixed the next day can show a visible line. One extra bag costs a few pounds; re-grouting a room costs a weekend.
Sanded vs unsanded grout
Pick by joint width first, then by surface. Using the wrong one causes cracking or scratching.
| Type | Joint width | Best for | Watch out for |
|---|---|---|---|
| Unsanded | Under 1/8 in | Wall tile, polished stone, glass | Cracks in wide joints as it shrinks |
| Sanded | 1/8 in and wider | Floors, most ceramic and porcelain | Sand can scratch polished marble |
| Epoxy | Any | Wet areas, worktops, heavy stain risk | Short working time, costs far more |
| Single-component | Any | DIY, no mixing, stain resistant | Slow cure, premium price |
Worked example: grouting a 12 × 12 ft floor
A 144 ft² floor in 12 × 12 in porcelain, 3/8 in thick, with 1/8 in joints.
| Step | Working | Result |
|---|---|---|
| From the chart | 7.7 lb per 100 ft² | — |
| Scale to the floor | 7.7 × 1.44 | 11.1 lb |
| Add 20% waste | 11.1 × 1.20 | 13.3 lb |
| In 25 lb bags | 13.3 ÷ 25 | 1 bag |
| In 10 lb bags | 13.3 ÷ 10 | 2 bags |
One 25 lb bag covers this comfortably. Change the tile to 4 × 4 in and the same floor needs about 32 lb, or two bags — the floor did not change, only the joint length did.
What grout costs
Standard sanded or unsanded cement grout runs roughly $15 to $25 for a 25 lb bag. Premium single-component grouts cost $30 to $60 for the same weight, and epoxy grout is the most expensive at $60 to $120 per unit, though it resists staining far better in showers and on worktops.
Budget for the extras too: a grout float, a large sponge, two buckets, grout sealer for cement-based products, and silicone for the corners and edges where grout would crack.
Grout mistakes that ruin a floor
- Estimating from floor area alone. Tile size changes the answer by ten times.
- Running short mid-job. Colour varies between mixes, so a second batch can show a line.
- Sanded grout on polished marble. The sand scratches the surface permanently.
- Unsanded grout in wide joints. It shrinks and cracks as it cures.
- Too much water in the mix. Weak, powdery, patchy-coloured joints.
- Grouting the corners. Wall-to-floor and internal corners move, so they need silicone, not grout.
- Washing too soon or too wet. Pulls grout out of the joint and leaves haze on the tile.
How this grout calculator works out its numbers
Grout volume is exact geometry. In a grid of A × B tiles with joint width C, each repeating cell is (A+C)(B+C); subtract the tile face for joint area, multiply by joint depth (your tile thickness) for volume, then by density for weight. Density is taken as 120 lb/ft³.
- Waste defaults to 20%, higher than elsewhere on this site, because grout lost in the bucket, on the float and in the sponge is a genuinely large share of what you mix.
- Manufacturer charts disagree by 2 to 3× for identical tile. The geometry here matches the sourced figures that agree with each other (a 25 lb bag covering roughly 340 ft² of 12×12 in tile equals 7.35 lb per 100 ft²; this calculator gives 7.7 at a realistic 3/8 in thickness). More conservative charts build in the site loss described above. If your bag's chart is more conservative, follow the bag.
Figures reviewed . Every worked example on this page is checked against the calculator above.
Grout Calculator: frequently asked questions
How much grout do I need per square foot?
For 12x12 in tile with 1/8 in joints, about 0.077 lb per square foot, or 7.7 lb per 100 ft², before waste. Small mosaic at the same joint width needs around 52 lb per 100 ft², because joint length per square foot is far higher.
How many square feet does a 25 lb bag of grout cover?
Roughly 300 to 340 ft² of 12x12 in tile with 1/8 in joints, before waste, or about 250 to 280 ft² once you allow 20% for mixing and cleanup loss. For 4x4 in tile the same bag covers only about 110 ft².
Should I use sanded or unsanded grout?
Joint width decides it. Use unsanded for joints under 1/8 inch and sanded for 1/8 inch and wider. Unsanded cracks in wide joints as it shrinks; sanded can scratch polished marble and glass, so use unsanded or epoxy on those.
Why do grout coverage charts give different numbers?
The geometry is fixed, but manufacturers differ in how much site loss they assume. Grout left in the bucket, on the float and in the sponge is a genuine and large loss, so some charts quote two to three times the theoretical volume. This calculator shows geometry plus your chosen waste, defaulting to 20%.
How much grout do I need for a 12x12 room?
A 144 ft² floor in 12x12 in tile with 1/8 in joints needs about 11 lb of grout, or 13.3 lb with 20% waste, so one 25 lb bag. The same room in 4x4 in tile needs about 32 lb, or two bags.
Do wider grout joints use more grout?
Yes, and close to proportionally. Going from 1/8 to 1/4 inch roughly doubles the grout for the same tile. Tile thickness matters just as much, because the joint is as deep as the tile is thick.
How much does a bag of grout cost?
Standard cement grout runs about $15 to $25 per 25 lb bag. Single-component grouts cost $30 to $60, and epoxy grout $60 to $120, though epoxy resists staining much better in showers and on worktops.
How many square feet does a 10 lb bag of grout cover?
About 108 ft² of 12x12 in tile with 1/8 in joints, allowing 20% waste. A 25 lb bag covers roughly 271 ft² of the same tile. Switch to 4x4 in tile and that 25 lb bag covers only about 112 ft², because joint length per square foot more than doubles.
How much grout do I need for 50 square feet?
About 4.6 lb for 12x12 in tile with 1/8 in joints including waste, so a single 10 lb bag is plenty. The same 50 ft² in 4x4 in tile needs about 11 lb, which means a 25 lb bag.
Should grout sit flush with the tile?
Level with the tile edge, not proud of it. A slightly concave joint is normal and sheds water. Overfilled joints smeared across the tile face trap dirt and chip; joints filled to less than two thirds of the tile depth are weak and let water through.