Grout Calculator
Grout = joint length per ft² × area × joint width × tile thickness × ~105 lb/ft³. 12 × 12 in tile has 2 ft of joint per ft², so 100 ft² with 1/8 in joints and 3/8 in tile needs 6.8 lb — 7.6 lb with 10% waste, one 25 lb bag. Count the tiles with the Tile Calculator.
How it's calculated: Joint length per ft² = (tile L + tile W) ÷ (tile L × tile W); grout volume = joint length × area × joint width × tile thickness; weight = volume × ~105 lb/ft³, plus waste; bags = weight ÷ bag size, rounded up.
Result appears here
Fill in the fields and press Calculate.
Formula, calculation, assumptions and sources
Joint length per ft² = (tile L + tile W) ÷ (tile L × tile W)
Grout volume = joint length per ft² × area × joint width × tile thickness
Grout weight = volume × ~105 lb/ft³ (dry sanded grout)
Run the calculation to see each step with your own numbers.
100 ft² of 12×12 in tile, 1/8 in joints, 3/8 in thick, 25 lb bags, 10% waste.
Joint length = (1 ft + 1 ft) ÷ (1 ft × 1 ft) = 2 ft per ft² → 200 ft over 100 ft²
Volume = 200 ft × (0.125/12) ft × (0.375/12) ft ≈ 0.065 ft³
≈ 0.065 ft³ × 105 lb/ft³ ≈ 6.8 lb exact → order 7.6 lb with 10% → 1 bag of 25 lb
- Square/rectangular tile in a grid layout; grout fills the joint to about the tile thickness.
- Dry sanded-grout density ~105 lb/ft³ — unsanded grout is slightly less dense.
- Very small mosaic tile or very wide joints use noticeably more grout — the formula accounts for both.
- Sanded or unsanded grout?
- Use sanded for joints 1/8 in and wider, unsanded for narrower joints and polished/soft stone that sand would scratch. The quantity is nearly the same.
- Why does tile size change how much grout I need?
- Grout fills the joints between tiles, and a floor of small tiles has far more joint length per square foot than a floor of large tiles — so at the same joint width it uses several times more grout.
- How deep does the grout fill?
- To roughly the tile thickness, which is why the calculator asks for it. A thick paver or stone tile takes more grout per foot of joint than a thin wall tile.
- How much grout do I need for 100 square feet of 12×12 tile?
- About 6.8 lb with 1/8 in joints and 3/8 in thick tile, or 7.6 lb with 10% waste — one 25 lb bag. The same floor in 6 × 6 in tile has twice the joint length, 4 ft per ft², and needs about 13.7 lb, or 15.1 lb with waste.
Coverage formula
Standard grout-coverage geometry; matches the grout-manufacturer coverage charts (Custom Building Products, Mapei, Laticrete).
Grout density
Dry sanded grout ≈ 100–110 lb/ft³ (≈ 1,680 kg/m³). Grout-manufacturer data (Custom Building Products, Mapei, Laticrete coverage charts).
About the Grout Calculator
The Grout Calculator estimates how much grout a tiled area needs — as a weight and a bag count — from the tile size, the joint width and the tile thickness. Smaller tiles and wider joints mean more linear feet of joint per square foot, so the quantity climbs; a large-format floor with tight joints uses very little. Thinset and the tile count itself are separate calculations.
What you enter
- Tiled area
- Tile length
- Tile width
- Grout joint width — 1/16–1/8 in for wall tile; 3/16–1/4 in for floor and stone.
- Tile thickness — The grout fills to roughly the tile thickness.
- Bag size (lb)
- Waste allowance — Covers grout left in the bucket and the joints you'll re-grout.
What you get back
- Grout needed — shown as the exact figure and, separately, a recommended figure with your waste allowance added.
- Bags — the exact result of the calculation.
The formula, a worked example, the assumptions behind it and the sources are shown in full below the calculator.
Related calculators
- Tile Calculator — Tiles and boxes needed for a floor or wall, including an allowance for cuts.
- Thinset Calculator — Thinset mortar quantity for a tiled area from tile size and trowel notch.
- Floor Area Calculator — Total floor area of a room or a set of rooms.
Related articles
- Tile, Grout and Thinset: What Does Each Material Do? — Tile is the finished surface, thinset bonds it to the substrate, and grout fills the joints between tiles — each calculated a different way.
Part of the Tile & Flooring calculators.