Grout Calculator
Calculate how many pounds and bags of grout you need from the tile size, tile thickness, joint width and area. Works for floors, walls and backsplashes.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Grout needed
- 5.9 lb
- Including 15% waste. Manufacturer coverage charts run more conservative, so check the bag.
- 10 lb bags to buy
- 1 bag
- 10 lb purchased
- Grout without waste
- 5.1 lb
- 0.05 cu ft of joints at 0.125 in wide and 0.375 in deep
- Tiles covered
- 78 tiles
- 12 in x 12 in tile over 80 sq ft
Grout formula
Tiles = Area (sq in) / ((Tile width + joint) x (Tile length + joint))
Joint volume (cu in) = Tiles x (Tile width + Tile length) x joint width x tile thickness
Grout (lb) = Joint volume x 0.0578 lb per cu in x (1 + waste %)
Bags = Grout (lb) / bag size, rounded upWorked example
A 12 x 12 ft kitchen floor in 12 x 24 in porcelain, 3/8 in thick with 3/16 in joints: 144 sq ft x 144 = 20,736 sq in. Each tile occupies 12.1875 x 24.1875 = 294.8 sq in, so there are 70.3 tiles. Joint volume = 70.3 x (12 + 24) x 0.1875 x 0.375 = 178 cu in.
Grout = 178 x 0.0578 = 10.3 lb, plus 15% waste = 11.8 lb. Buy one 25 lb bag or two 10 lb bags.
Quick reference
| Tile size | Tiles per 100 sq ft | Grout |
|---|---|---|
| 3 x 6 in | 752 | 18.4 lb |
| 4 x 4 in | 846 | 18.3 lb |
| 6 x 6 in | 384 | 12.5 lb |
| 12 x 12 in | 98 | 6.4 lb |
| 12 x 24 in | 49 | 4.8 lb |
| 18 x 18 in | 44 | 4.3 lb |
| 24 x 24 in | 25 | 3.2 lb |
How to calculate grout
Grout fills the joints between tiles, so the amount depends on the total joint length, the joint width and the tile thickness, not just the floor area. Small tiles like 3 x 6 subway or 4 x 4 have far more joint per square foot than 12 x 24 planks: about 18 lb per 100 sq ft versus 5 lb. Thicker tile and wider joints scale the amount up in proportion.
This calculator works from the joint geometry and a dry density of about 100 lb per cubic foot. Manufacturer coverage charts assume more waste and fuller joints and usually show less coverage per bag, so if the chart on the bag disagrees, trust the chart. Grout is inexpensive, and an opened bag keeps for months if sealed and dry.
Sanded, unsanded and epoxy grout
Sanded cement grout is for joints 1/8 inch and wider; the sand keeps it from shrinking and cracking. Unsanded grout is for joints under 1/8 inch and for polished stone or glass that sand would scratch. Both come in 10 and 25 lb bags, and the 25 lb bag is usually the better value for a floor.
Epoxy and premixed urethane grouts are sold by the gallon or in small tubs and have their own coverage charts. They resist stains and do not need sealing, but they cost several times more and set faster, so mix small batches. Cement grout should be damp-cured and then sealed after 48 to 72 hours.
Key facts
- Use sanded grout for joints 1/8 in and wider and unsanded grout for joints narrower than 1/8 in.
- Dry grout weighs about 100 lb per cubic foot, so 1 lb fills about 17 cubic inches of joint.
- Larger tiles need far less grout: 12 x 12 in tile takes about 6.4 lb per 100 sq ft, 4 x 4 in tile about 18 lb, at 1/8 in joints.
- Typical joint widths are 1/16 in for rectified porcelain, 1/8 to 3/16 in for ceramic and 1/4 in for natural stone.
- Cement grout should cure 48 to 72 hours before it is sealed.
Frequently asked questions
How much grout do I need for 100 square feet of 12x12 tile?
About 6.4 lb with 1/8 inch joints and 3/8 inch thick tile, or 7.3 lb with 15% waste. One 10 lb bag covers it.
How much does a 25 lb bag of grout cover?
It depends on the tile. At 1/8 inch joints, a 25 lb bag covers about 340 sq ft of 12 x 12 in tile but only about 120 sq ft of 4 x 4 in tile, both with 15% waste. Manufacturer charts are more conservative and often show about half those figures.
Should I use sanded or unsanded grout?
Sanded for joints 1/8 inch and wider, unsanded for narrower joints and for soft or polished surfaces like marble and glass that sand can scratch.
How long before grout can get wet?
Keep it dry for 24 hours and avoid heavy use for 72 hours. Apply a penetrating sealer to cement grout after 48 to 72 hours of curing.
Sources and references
- Polyblend Plus Sanded Grout coverage chart by tile size and joint width (Custom Building Products)
- Polyblend Sanded Grout technical data sheet TDS-129 (Custom Building Products)
- Ultracolor Plus FA grout product page and coverage (Mapei)
Next steps for this project
The usual order for a flooring & tile project. See all flooring & tile calculators.
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.