Grout calculator
This estimates grout from clean joint geometry and a density you set. Real coverage shifts with mixing, how full you pack the joints and the trowel work, so it runs generous on purpose — round up, and mix a full bag rather than stopping a job to open another.
Enter the tiled area, the tile size, the joint width and the tile thickness. The tool finds the grout volume per unit of area from the joint geometry, multiplies by the area, then turns that volume into a weight and a bag count using the density and bag size you enter.
Exemple détaillé
A 10 ft × 10 ft floor is 100 sq ft in 12-inch tiles, 5/16 inch thick, with a 3/16 inch joint. The grout per square foot works out to a thin film — about 0.0008 ft³ — so the floor takes roughly 0.08 ft³ of grout, near 7 lb, comfortably inside one 25 lb bag. Switch to 2-inch mosaic and the same floor jumps past a full bag.
In metric: 9.3 m² of 300 × 300 mm tile, 8 mm thick, with a 5 mm joint. The joint runs (0.3 + 0.3) ÷ (0.3 × 0.3) = 6.67 m per square metre, so the grout is 6.67 × 0.005 × 0.008 = 0.00027 m³ a square metre, 0.0025 m³ for the floor — at 1440 kg/m³ about 3.6 kg, inside one 11 kg bag.
Sur le chantier
It is the joint length that gets you. A 12 in tile has 2 ft of joint under every square foot of floor; a 2 in mosaic has 12 ft. Same joint width, same depth, six times the grout: the 100 ft² floor in 2 in mosaic at a 3/16 joint and 5/16 deep is 0.49 ft³, about 44 lb, two 25 lb bags where the 12 in tile took seven pounds. Sheet mosaics are where the grout budget lives. (In metric a 50 mm mosaic has 40 m of joint under every square metre; a 300 mm tile has 6.7 m.)
Big tile, tight joint. 200 ft² of 12 × 24 at a ⅛ in joint, ⅜ in thick: joint length (12 + 24) ÷ (12 × 24) = 0.125 in per in², × 0.125 × 0.375 = 0.0059 in³ per in² of floor — 0.84 in³ per ft², 169 in³ for the room, a tenth of a cubic foot, under 9 lb. One bag, and most of it left over. In metric, 300 × 600 mm at a 3 mm joint, 10 mm thick, is (0.3 + 0.6) ÷ 0.18 = 5 m of joint per m², × 0.003 × 0.01 = 0.00015 m³ — about 0.2 kg a square metre.
Depth is the tile, not the joint. Grout fills the joint to the tile's thickness (less what the thinset squeezed up). Type the tile thickness off the box; a ⅜ tile takes 20% more grout than a 5/16 at the same joint. The bag tells you which joint widths it is made for — that is the maker's call, not a number this page decides.
What went wrong?
Quick referencefor grout
- Joint length per ft² of floor
- 12 in tile 2 ft · 6 in 4 ft · 4 in 6 ft · 2 in 12 ft · 12 × 24 1.5 ft · 3 × 6 6 ft
- Grout volume
- joint length × joint width × tile thickness
- Unités
- 1,728 in³ in a ft³ · at 90 lb/ft³ a 25 lb bag is about 0.28 ft³ (480 in³)
- 100 ft² at 3/16 × 5/16
- 12 in tile 7 lb · 6 in 14 lb · 4 in 22 lb · 2 in 44 lb
- Métrique
- 30 cm tile: 6.7 m of joint per m² · 1440 kg/m³ is the same 90 lb/ft³
- 10 m² at 5 × 8 mm, 1440 kg/m³
- 300 mm tile 3.8 kg · 150 mm 7.7 kg · 100 mm 11.5 kg · 50 mm 23 kg
Waste & overagewhat to add, and why
- Tilers buy a bag beyond the count — grout that sets in the bucket, the first mix that goes too wet, and the wipe-off all take their share. A 10% margin on the pounds is normal.
- Keep one full bag of the same colour and batch for repairs; grout colours drift between production runs.
Mistakes to catchbefore you order
- Typing the joint width as the tile spacing across the room instead of the gap between two tiles — the tool wants the joint width in inches or mm.
- Using the tile's rated thickness when the grout joint is only filled to the top of a bevelled edge; the joint depth is what the grout fills, and a thick tile with a deep bevel takes less.
- Forgetting that mosaic sheets are hundreds of tiny joints — the joint length per square foot is huge, and the grout quantity with it.
La formule
grout per area = ((tile L + tile W) ÷ (tile L × tile W)) × joint width × thickness
With the tile dimensions in the joint's own length unit, that expression has units of length — it is the grout volume for each unit of tiled area. Multiply by the area to get a volume, by the density for a weight, and divide by the bag size for the count. The tile size in the denominator is why mosaics drink grout.
Questions
- How much grout do I need for a tile job?
- It comes from the joints, not the tiles: the smaller the tile, the more joint per square foot, and a wider or deeper joint fills faster. This tool takes your tile size, joint width and tile thickness, works out the volume of grout per unit of area, multiplies by the floor or wall area and turns it into a weight and a bag count.
- Why does small tile use so much more grout?
- A mosaic has a joint around every little tile, so there is far more total joint length in a square foot than there is with a large-format tile. Because the grout volume tracks that joint length, halving the tile size roughly doubles the grout. The formula shows it directly — the tile dimensions sit in the denominator.
- What density and bag size should I enter?
- Both are on the product. Mixed grout is roughly 90 pounds per cubic foot, near 1440 kilograms per cubic metre, and those are the editable defaults — a sanded grout runs a little heavier. Bags are commonly 25 pounds or about 11 kilograms. Use the figures from the bag in front of you for the closest count.
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