Grout calculator
Grout calculator for pounds and bags of sanded grout.
Enter the tiled area, tile size, joint width, and tile thickness to get pounds of sanded grout and how many bags to buy. 100 sq ft of 12 x 12 in tile with 1/8 in joints takes about 7.9 lb.
100 sq ft, 12 x 12 tile, 1/8 in joint
7.9 lb
1 bag of 25 lb
Same floor, 1/4 in joint
15.6 lb
twice the joint, about twice the grout
3 x 6 subway tile, 1/8 in joint
15.3 lb
small tile means more joints
Quick reference
Square feet one 25 lb bag of sanded grout covers
Coverage by tile size and joint width, with the joint as deep as the tile is thick. No waste included.
| Tile size | 1/8 in joint | 3/16 in joint | 1/4 in joint | 3/8 in joint |
|---|---|---|---|---|
| 3 x 6 x 1/4 in | 179 sq ft | 122 sq ft | 94 sq ft | 65 sq ft |
| 6 x 6 x 1/4 in | 264 sq ft | 179 sq ft | 136 sq ft | 94 sq ft |
| 12 x 12 x 3/8 in | 347 sq ft | 233 sq ft | 176 sq ft | 119 sq ft |
| 6 x 24 x 3/8 in | 279 sq ft | 188 sq ft | 143 sq ft | 97 sq ft |
| 12 x 24 x 3/8 in | 461 sq ft | 309 sq ft | 233 sq ft | 158 sq ft |
| 24 x 24 x 3/8 in | 689 sq ft | 461 sq ft | 347 sq ft | 233 sq ft |
Checked against the charts
This calculator vs manufacturer coverage charts
Square feet per 25 lb bag on 12 x 12 x 3/8 in tile. The chart rows are the numbers printed in each manufacturer's data sheet; the calculator row is computed from the formula below.
| Joint width | 1/8 in | 3/16 in | 1/4 in | 3/8 in | 1/2 in |
|---|---|---|---|---|---|
| This calculator | 347 | 233 | 176 | 119 | 91 |
| Custom Polyblend Plus chart | 348 | 234 | 177 | 121 | 92 |
| MAPEI Keracolor S chart | 383 | 253 | 191 | 126 | 94 |
Why the charts differ
Products differ in density and each maker works out coverage a little differently, so two sanded grouts can differ by about 10% on the same floor. The calculator follows the lower-coverage chart.
Formula shown
How the grout estimate works
1. Joint share of the surface
share = 1 - (L x W) / ((L + J) x (W + J))
2. Joint volume
volume (in³) = area (sq ft) x 144 x share x tile thickness
3. Pounds and bags
pounds = volume x 0.065 lb per in³ x (1 + waste); bags = ceil(pounds / bag size)
Worked example: 100 sq ft of 12 x 12 x 3/8 in tile, 1/8 in joints
Joint share is 1 - 144 / (12.125 x 12.125) = 2.05%. Joint volume is 100 x 144 x 0.0205 x 0.375 = 111 in³. At 0.065 lb per in³ that is 7.2 lb, or 7.9 lb with 10% waste.
What this does not include
Unsanded and epoxy grout, grout lost to very uneven or handmade tile, caulk for movement joints at walls and changes of plane, and sealer. Mix only what you can place before it stiffens, and keep one color lot for the whole job.
Next step
Finish the tile estimate
Sources
- Custom Building Products Polyblend Plus Sanded Grout data sheet (TDS-360) — coverage chart per 25 lb and 7 lb bag by tile size and joint width (published March 2023)
- MAPEI Keracolor S Sanded Grout data sheet — approximate coverage per 25 lb by tile size and joint width (February 2026)
Sources checked
Checked against
Usage factor back-calculated from manufacturer grout coverage charts (Custom Building Products, MAPEI).
How we check our numbersLast updated: October 4, 2026
FAQ
Grout calculator questions
How much grout for 100 square feet, the grout formula, bag coverage, tile thickness, and how the estimate compares with manufacturer charts.
How much grout do I need for 100 square feet? + -
For 12 x 12 in tile that is 3/8 in thick with 1/8 in joints, 100 sq ft takes about 7.2 lb of sanded grout, or 7.9 lb with 10% waste: one 25 lb bag with plenty left over. The same floor with 1/4 in joints takes about 15.6 lb, and 3 x 6 in subway tile with 1/8 in joints about 15.3 lb.
How do you calculate grout? + -
Find the share of the surface that is joint: 1 minus tile length times tile width, divided by (length plus joint) times (width plus joint). Multiply that by the area in square inches and the joint depth to get the joint volume, then by the pounds of dry grout needed per cubic inch of joint. Smaller tiles, wider joints, and thicker tiles all need more grout.
How many square feet does a 25 lb bag of grout cover? + -
It depends on the tile and joint. On 12 x 12 x 3/8 in tile, a 25 lb bag of sanded grout covers about 347 sq ft with 1/8 in joints and about 176 sq ft with 1/4 in joints. On 3 x 6 in subway tile with 1/8 in joints it covers about 179 sq ft.
Why does tile thickness matter? + -
Grout fills the joint to the full depth of the tile, so the tile thickness is the joint depth. A 1/2 in thick tile takes about a third more grout than a 3/8 in tile at the same size and joint width.
Does this work for unsanded or epoxy grout? + -
No. The usage factor here comes from sanded cement grout coverage charts. Unsanded grout is for joints under 1/8 in, and epoxy grout is sold by unit with its own coverage chart. For those, use the chart on the product.
How close is this to the manufacturer chart? + -
For 12 x 12 x 3/8 in tile with 1/8 in joints, this calculator gives 347 sq ft per 25 lb bag. The Custom Polyblend Plus chart prints 348 sq ft and the MAPEI Keracolor S chart prints 383 sq ft. The calculator follows the lower-coverage chart of the two.