How the grout calculator works
Grout coverage depends heavily on tile size, tile thickness, and joint width, and each manufacturer publishes a chart. The calculator takes the tiled area, adds your allowance, divides by the coverage per bag from that chart, and rounds up.
The chart shows how much of the bags you will use and how much is left in the last bag.
Formula and assumptions
- coverage per bag
- from your grout chart for your tile and joint size
Assumptions and limits
- The 348 sq ft default is a single named product example, valid only for that tile and joint size.
- Coverage is not converted between powder and premixed products.
Worked example
100 sq ft of tile and a chart coverage of 348 sq ft per bag (one sanded grout’s 25 lb figure for 12 × 12 in tile with 1/8 in joints), plus 10%.
- 100 × 1.10 = 110 sq ft.
- 110 ÷ 348 = 0.32 bags.
- Round up: buy 1 bag.
These are the calculator’s default values, so the live result above matches this example until you change an input.
How to measure correctly
- Find the row in the grout chart for your exact tile size, thickness, and joint width.
- Mosaics and small tiles have far more joint length per square foot; coverage drops sharply.
- Do not reuse one product’s coverage for another brand or bag size.
Grout Calculator FAQ
How much grout do I need?
Look up your tile size and joint width in the grout manufacturer’s coverage chart, divide your area (plus a small allowance) by that coverage, and round up to whole bags.
Why does small tile need so much more grout?
Smaller tiles mean more joints per square foot. A mosaic floor can need many times the grout of the same area in large tile.
How much extra grout should I buy?
MAPEI suggests a 5–10% overage for its products. Leftover grout from the same batch is also handy for repairs.
Sanded or unsanded grout?
It depends on joint width and tile surface. The manufacturer’s guidance decides; this calculator only handles quantity.
Can I use this for premixed grout tubs?
Yes, if you enter the tub’s coverage for your tile and joint size from the label.