How much grout you need depends less on the floor area than on the joints: small tiles have many more joints per square foot than large tiles, and wide, deep joints hold more grout. This grout calculator measures the joint volume per square foot from your tile size, thickness and joint width, converts it to pounds of sanded grout and rounds up to whole bags. For example, 150 ft² of 12 × 24 × 3/8 inch tile with 3/16 inch joints takes about 13 lb, a single 25 lb bag, while the same floor in 2 inch mosaics would take more than five times as much.
Count the tile itself with the tile calculator, and the mortar underneath with the thinset calculator.
How to use the grout calculator
- Enter the length and width of the tiled area (for walls, the wall height and width).
- Enter the tile length, width and thickness. The thickness sets the joint depth; use the actual thickness, not the nominal.
- Enter the joint width: commonly 1/16 to 1/8 inch for rectified tile and 3/16 to 1/4 inch or more for handmade or uneven tile. Sanded grout is generally used for joints of 1/8 inch and wider.
- Keep about 10% extra for mixing loss and cleanup, then choose your bag size.
Formula
The 0.064 lb per cubic inch factor reproduces the manufacturer's published coverage chart for a 25 lb bag of sanded grout within a few percent for standard floor tiles (it gives 347 ft² for 12 × 12 × 3/8 inch tile with 1/8 inch joints, against a published 348 ft²).
Worked example
A 15 × 10 ft kitchen floor with 12 × 24 inch porcelain, 3/8 inch thick, 3/16 inch joints and 10% extra.
- Joint volume: 144 × (24 + 12) ÷ (24 × 12) × 0.1875 × 0.375 = 144 × 0.125 × 0.0703 = 1.27 in³ per ft².
- Pounds per ft²: 1.27 × 0.064 = 0.081 lb.
- Total: 150 × 0.081 × 1.10 = 13.4 lb, so one 25 lb bag.
- Coverage: one 25 lb bag covers about 309 ft² of this tile (the manufacturer's chart lists 310 ft²).
Grout coverage per 25 lb bag
Square feet covered by one 25 lb bag of sanded grout, computed with the formula above (no waste). For small mosaics the manufacturer's chart shows 10–20% more coverage than this simple joint model, so the estimate errs on the side of extra grout.
| Tile (W × L × thickness) | 1/8 in joint | 3/16 in joint | 1/4 in joint | 3/8 in joint |
|---|---|---|---|---|
| 2 × 2 × 1/4 in | 87 ft² | 58 ft² | 43 ft² | 29 ft² |
| 4.25 × 4.25 × 1/4 in | 184 ft² | 123 ft² | 92 ft² | 61 ft² |
| 6 × 6 × 1/4 in | 260 ft² | 174 ft² | 130 ft² | 87 ft² |
| 12 × 12 × 3/8 in | 347 ft² | 231 ft² | 174 ft² | 116 ft² |
| 12 × 24 × 3/8 in | 463 ft² | 309 ft² | 231 ft² | 154 ft² |
| 18 × 18 × 3/8 in | 521 ft² | 347 ft² | 260 ft² | 174 ft² |
| 24 × 24 × 3/8 in | 694 ft² | 463 ft² | 347 ft² | 231 ft² |
| 6 × 36 × 3/8 in | 298 ft² | 198 ft² | 149 ft² | 99 ft² |
Sanded, unsanded and epoxy grout
Sanded cement grout is the default for floor joints of about 1/8 inch and wider; the sand resists shrinkage and cracking in wide joints. Unsanded grout is for narrow joints, typically under 1/8 inch, and for surfaces that sand could scratch. Epoxy and single-component urethane grouts are denser and sold by volume in smaller units, so check the product's own coverage chart. Movement joints at the perimeter and changes of plane get flexible sealant, not grout; the caulk calculator counts tubes.
Caveats and assumptions
- The density factor is calibrated to standard sanded cement grout. Lightweight, unsanded, urethane and epoxy grouts cover differently.
- Tiles with cushioned or pillowed edges hold more grout than square-edged tiles of the same thickness.
- Mix only what you can use in the working time on the bag; leftover mixed grout can't be saved.
- Wall tile is usually thinner than floor tile; enter the actual thickness.
Frequently asked questions
How much grout do I need for 100 square feet?
For 12 × 12 × 3/8 inch tile with 1/8 inch joints, about 7.2 lb, so a 10 lb bag. For 2 × 2 mosaics with 1/8 inch joints, about 29 lb, so two 25 lb bags.
How many square feet does a 25 lb bag of grout cover?
It ranges from about 40 ft² for small mosaics with wide joints to about 700 ft² for 24 × 24 tile with 1/8 inch joints. For 12 × 12 tile with 1/8 inch joints, about 348 ft².
How much grout for 12x24 tile?
With 3/8 inch thick tile, about 0.054 lb per ft² at 1/8 inch joints and 0.081 lb per ft² at 3/16 inch joints, so one 25 lb bag covers roughly 460 or 310 ft².
Does joint width really change grout amount that much?
Yes. Grout volume is proportional to joint width, so 1/4 inch joints use twice as much grout as 1/8 inch joints with the same tile.
When should I use sanded vs unsanded grout?
Sanded grout is generally recommended for joints 1/8 inch and wider, unsanded for narrower joints. Always follow the grout manufacturer's joint-width range.
Sources
- Custom Building Products — Polyblend Sanded Grout coverage chart — coverage per 25 lb bag by tile size and joint width
- Tile Council of North America — TCNA Handbook and ANSI A108 installation standards
- NIST — Unit Conversion — inch and millimetre conversion
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.