Grout Calculator
This grout calculator works out how much tile grout a floor or wall needs from the tile size, joint width and tile thickness, the three things that set the quantity.
Grout Needed
Joint Width Comparison
Joint width and tile size both move the quantity a long way. This shows how far.
Grout Cost
How to use the Grout Calculator
Enter the tiled area, then the tile’s face dimensions and its thickness, thickness matters because the joint is a channel with depth, not a line on a drawing.
Then the joint width. This is the input that moves the answer most: going from ⅛ in to ¼ in doubles the grout, and going from a 12 in tile to a 3 in mosaic at the same joint width roughly quadruples it.
The Compare panel is there for when the joint width has not been decided yet.
Grout Cost takes the bag size you can actually buy locally and adds sealer, which is easy to leave out of an estimate and is priced by coverage rather than by the bag.
Grout formula
Grout quantity is the volume of the joints multiplied by the density of the grout. Nothing else.
share of floor that is joint = ((L + J)(W + J) − L × W) ÷ ((L + J)(W + J))joint volume per sq ft = 144 × that share × Tcubic incheslb per sq ft = joint volume × density ÷ 1,728
with L, W the tile face in inches, T the tile thickness, J the joint width. One tile plus its share of joint occupies (L + J) × (W + J), that is the tile pitch, and everything follows from it.
Densities are back-solved from published manufacturer coverage charts: 110 lb/ft³ for sanded, 100 for unsanded, 72 for lightweight high-yield grouts. Reproducing CUSTOM’s chart for a 12 × 12 × ⅜ in tile at a ⅛ in joint gives 349 sq ft per 25 lb bag against their published 348, a third of one percent.
| Tile | ⅛ in joint | ¼ in joint |
|---|---|---|
| 12 × 12 × ⅜ in | 0.071 lb/sq ft | 0.139 lb/sq ft |
| 6 × 6 × ⅜ in | 0.139 lb/sq ft | 0.270 lb/sq ft |
| 3 × 3 × ¼ in | 0.180 lb/sq ft | 0.339 lb/sq ft |
| 24 × 12 × ⅜ in | 0.053 lb/sq ft | 0.105 lb/sq ft |
Bag charts use a simplified joint term that ignores the joint in the tile pitch. It runs about two percent high on a 12 in tile and nearer ten percent high on a small mosaic, so it always errs toward ordering more. The tool shows both figures side by side.
Worked example
200 sq ft of 12 × 12 in tile, ⅜ in thick, with ⅛ in joints:
- Tile plus its joint: 12.125 × 12.125 = 147.02 sq in
- Share of the floor that is joint: (147.02 − 144) ÷ 147.02 = 2.05%
- Joint volume: 144 × 0.0205 × 0.375 = 1.11 cu in per sq ft
- At 110 lb/ft³ sanded: 1.11 × 110 ÷ 1,728 = 0.071 lb per sq ft
- 200 × 0.071 = 14.1 lb, plus 10% = 15.5 → 2 ten-pound bags
The same floor in 6 × 6 tile needs about 28 lb, four bags, for exactly the same square footage.
What the result means
Small tiles drink grout. Halving the tile size doubles the joint length per square foot and doubles the grout. A mosaic sheet can need six or eight times what a large-format tile needs.
Sanded or unsanded is set by the joint, not by preference. Joints ⅛ in and wider take sanded grout; narrower than that takes unsanded, because the sand will not pack into the gap. Some polished and soft stone tiles scratch under sanded grout regardless of joint width.
Buy it in one lot. Cementitious grout colour varies between production batches, and a colour change halfway across a floor is permanent.
Common mistakes
- Ignoring tile thickness. The joint is a channel. A ⅝ in porcelain paver needs two-thirds more grout than a ⅜ in tile at the same joint width.
- Mixing more than you can use. Cementitious grout starts setting in about half an hour. Mix in small batches.
- Adding water to loosen a stiffening batch. It ruins the colour and weakens the joint. Throw it out and mix fresh.
- Washing too soon or too wet. Both pull cement out of the joint and leave it pitted and pale.
- Assuming epoxy grout works out the same. Epoxy has a different density and its own coverage chart. Use the manufacturer’s figure.
Frequently asked questions
How much grout do I need for 200 square feet?
For 12 by 12 inch tile three eighths thick with eighth inch joints, about 14 pounds, so two ten pound bags with waste. The same 200 square feet in 6 by 6 tile needs roughly 28 pounds, because there is twice as much joint.
How do you calculate grout coverage?
Work out the area of one tile plus its joint, subtract the tile itself, and divide by the first figure. That is the share of the floor made of joint. Multiply by 144 and by the tile thickness for cubic inches per square foot, then by the grout density and divide by 1,728 for pounds. Multiply by your area and add ten percent.
Should I use sanded or unsanded grout?
Sanded for joints an eighth of an inch and wider, unsanded for anything narrower. The sand gives wide joints strength and stops them shrinking, but it will not compact into a narrow gap. Polished stone and some glass tiles want unsanded regardless, because sand scratches them.
Does joint width change how much grout I need?
A great deal. Grout quantity is directly proportional to joint width, so a quarter inch joint takes exactly twice what an eighth inch joint takes on the same tile. It is the single biggest variable after tile size.
How many bags of grout for a shower?
A typical three wall shower is about 100 square feet of wall. In 3 by 6 subway tile a quarter inch thick with sixteenth inch joints that is roughly 6 pounds, so one ten pound bag. Add a bag if the floor is mosaic, which drinks far more.
Do I need to seal grout?
Cementitious grout is porous and benefits from a penetrating sealer, particularly on floors and in showers. Wait for the cure time on the bag, usually about 72 hours. Epoxy grout does not need sealing.
Sources and assumptions
Densities are back-solved from published manufacturer coverage charts. CUSTOM Building Products Polyblend Sanded (TDS-129) gives 348 sq ft per 25 lb bag for a 12 × 12 × ⅜ in tile at a ⅛ in joint, and 234 sq ft at &frac316; in; both rows imply about 110 lb/ft³. MAPEI Keracolor S implies nearer 100, which is the figure used for unsanded. CUSTOM Prism and other lightweight high-yield grouts run nearer 72.
A widely circulated coverage constant of 14.5 implies a grout density of 174 lb/ft³, heavier than normal-weight concrete. No manufacturer publishes it. This page does not use it.
The ten percent waste allowance is separate and follows manufacturer guidance; LATICRETE recommends roughly ten percent extra for jobsite waste.
Sanded versus unsanded follows the Tile Council of North America: joints below ⅛ in take unsanded, ⅛ in and wider take sanded. Modern fine-aggregate products such as PERMACOLOR Select and Polyblend HP cover a wider range, use the joint range printed on the bag. Polished stone and some glass should not be grouted with sanded grout at any joint width.
Epoxy and urethane grouts have different densities and their own charts. Use the figure on the product.
This tool estimates material. Substrate movement joints, colour selection and cure times are not covered.
The density figures are back-solved from published coverage charts, see CUSTOM Polyblend Plus Sanded Grout for the chart this was checked against.