Grout calculator: how much grout do I need?
Grout depends on tile size, thickness and joint width, not just area. By CUSTOM's published chart, a 25 lb bag of sanded grout covers 348 square feet of 12 x 12 inch tile with 1/8 inch joints, but only 138 square feet of 3 x 3 inch tile. Small tiles and wide joints need far more.
Updated · By the Interior Redesign AI editorial team · Sources cited on the page
Sanded grout to buy
1 × 25 lb bag
7.9 lb needed, about $15.
| Coverage per 25 lb bag | 348 sq ft (maker's chart) |
|---|---|
| Grout for the area | 7.2 lb |
| With 10% extra | 7.9 lb |
| Bags | 1 |
| Cost | $15 |
Coverage is read straight from CUSTOM's published Polyblend Plus sanded grout chart, which the maker labels as an estimate. Sanded grout suits 1/8 to 1/2 in joints; other brands and unsanded or epoxy grouts cover differently, so check the bag. The 10% extra and the $14.98 bag price are editable defaults.
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Key numbers
- 12 × 12 × 3/8 in tile, 1/8 in joint
- 348 sq ft per 25 lb bag
- 12 × 12 × 3/8 in tile, 1/4 in joint
- 177 sq ft per 25 lb bag
- 3 × 3 × 1/4 in tile, 1/8 in joint
- 138 sq ft per 25 lb bag
- 1 × 1 × 1/4 in mosaic, 1/8 in joint
- 54 sq ft per 25 lb bag
- Sanded grout joint range
- 1/8 to 1/2 in (CUSTOM Polyblend Plus)
- Price used
- $14.98 per 25 lb bag at Home Depot, Oct 26, 2026 (editable)
Worked example
A shower wall in 3 × 3 in tile
74 sq ft of 3 × 3 × 1/4 in tile with 1/8 in joints, 10% extra, $14.98 per bag.
- Chart: 3 × 3 × 1/4 in at 1/8 in covers 138 sq ft per 25 lb bag.
- Grout: 74 ÷ 138 × 25 = 13.4 lb.
- With 10% extra: 14.7 lb, so 1 bag.
- Cost: 1 × $14.98 = $15.
Buy 1 × 25 lb bag of sanded grout, about $15.
How we calculate
Grout makers do not publish a single formula; CUSTOM Building Products publishes a coverage chart instead, giving square feet per 25 lb bag of Polyblend Plus sanded grout for 16 tile sizes and five joint widths. When your tile is on the chart, we read the chart: pounds = area ÷ coverage × 25.
When it is not, we start from the chart row with the most similar joint geometry and scale it. At the same joint width, the grout per square foot grows with the tile's perimeter per face area and with its thickness, so coverage scales by (length × width) ÷ ((length + width) × thickness). That scaling is our estimate, and the tool labels it.
Assumption: we add 10% for mixing loss and cleanup by default; the maker says its chart is for estimating and coverage varies with installation. Bags round up, with at least one bag for any job. Other brands and unsanded or epoxy grouts cover differently, so check their charts.
Estimates, sources
Planning estimates and published guidelines, not quotes, designs or code rulings. Figures were checked on each source on the date shown. Local prices, your home and your jurisdiction's adopted code decide the real answer.
- Polyblend Plus Sanded Grout: coverage chart (CUSTOM Building Products, as of Oct 26, 2026): sq ft per 25 lb bag by tile size and joint width, e.g. 12 x 12 x 3/8 in tile: 348 (1/8 in joint), 234 (3/16), 177 (1/4), 121 (3/8), 92 (1/2); 3 x 3 x 1/4 in: 138 / 96 / 74 / 54 / 43; accommodates 1/8-1/2 in joints; chart for estimating purposes, coverage may vary
- Custom Building Products Polyblend Plus 25 lb. Sanded Grout (PBPG38625) (The Home Depot, as of Oct 26, 2026): $14.98 per 25 lb bag (online price shown for a California store; prices vary by store and color)
Grout coverage per 25 lb bag
Square feet per 25 lb bag of CUSTOM Polyblend Plus sanded grout, from the maker's chart. A 200 sq ft floor of 12 × 24 in tile at 1/8 in needs 1 bag; the same area of 1 × 1 in mosaic needs about 5.
Off the chart, 3 × 6 in subway tile 5/16 in thick at 1/8 in scales to about 147 sq ft per bag from the 3 × 3 in row: an estimate.
| Tile (W × L × thickness) | 1/8 in | 1/4 in | 1/2 in |
|---|---|---|---|
| 1 × 1 × 1/4 in | 54 | 33 | 24 |
| 3 × 3 × 1/4 in | 138 | 74 | 43 |
| 6 × 6 × 1/4 in | 266 | 139 | 75 |
| 12 × 12 × 3/8 in | 348 | 177 | 92 |
| 12 × 24 × 3/8 in | 461 | 234 | 121 |
| 24 × 24 × 3/8 in | 688 | 348 | 177 |
Why joint width changes everything
Going from a 1/8 in to a 1/2 in joint on 12 × 12 in tile cuts coverage from 348 to 92 sq ft per bag, nearly four times the grout. Small tiles have more joint per square foot, so mosaics use the most grout of all.
How to use this tool
Enter the area
Square feet of tile to grout: walls and floor together if they use the same grout.
Enter the tile
Width, length and thickness, or tap a common size.
Pick the joint
The spacer size you are using, from 1/8 to 1/2 in.
Read the bags
Pounds, 25 lb bags and the cost, with the chart row the answer came from.
Questions
How much grout do I need for 100 square feet?
It depends on the tile and joint. For 12 × 12 in tile with 1/8 in joints, 100 sq ft takes about 7 lb, one 25 lb bag. For 1 × 1 in mosaic with 1/8 in joints it takes about 46 lb: two bags, or three once you add 10% extra.
How many square feet does a 25 lb bag of grout cover?
From 24 sq ft (1 × 1 in mosaic, 1/2 in joints) to 688 sq ft (24 × 24 in tile, 1/8 in joints), by CUSTOM's Polyblend Plus chart.
Does tile thickness affect how much grout I need?
Yes. Grout fills the joint to the tile's full depth, so thicker tile takes more. The chart uses 1/4 in for small tiles and 3/8 in for larger ones.
Should I use sanded or unsanded grout?
Sanded grout is made for 1/8 in joints and wider; CUSTOM rates Polyblend Plus sanded for 1/8 to 1/2 in. Narrower joints usually call for unsanded grout. Follow the tile maker's advice for polished stone or glass.
How much extra grout should I buy?
We add 10% by default for mixing and cleanup, our assumption. The maker notes its chart is an estimate and coverage varies with installation practice.
Is the result exact for my brand?
No. The chart is for CUSTOM Polyblend Plus sanded grout. Other brands, unsanded and epoxy grouts publish their own coverage, so check the bag or the maker's chart.
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