Grout Calculator
Estimate how much grout to buy for a tiling job. Enter the tile size, the joint width and depth, and the area to tile, and the calculator uses the standard grout formula to give kilograms, pounds and the number of bags.
1.6 is typical for cement grout; check your product sheet.
How to use the Grout Calculator
- Pick your units: inches and pounds, or millimeters and kilograms.
- Enter the tile size and the joint width (spacer size). The joint depth is normally the tile thickness.
- Enter the area to tile and the bag size of your grout.
- Check the density on the product data sheet if you know it (1.6 kg/L is a typical cement grout value).
- Read the results: grout weight, bags and coverage, and compare other joint widths.
The grout formula
Grout fills a grid of joints. Per square meter of tiling, the length of joint is (A + B) ÷ (A × B) (with tile sides in mm, × 1000 to get meters), and each meter of joint holds width × depth of grout. So:
Grout (kg/m²) = (A + B) ÷ (A × B) × C × D × ρ
where A and B are the tile length and width (mm), C the joint width (mm), D the joint depth (mm) and ρ the grout density (kg/L, about 1.6). Multiply by the area in m² and add a waste allowance for mixing and cleanup.
Example: 300 × 300 mm tiles, 3 mm joints, 8 mm deep: (300 + 300) ÷ (300 × 300) × 3 × 8 × 1.6 = 0.256 kg/m². For 10 m² with 10% waste: 0.256 × 10 × 1.1 = 2.8 kg.
In imperial units, convert inches to mm (× 25.4) and square feet to m² (× 0.0929), or let the calculator do it.
Grout per 100 sq ft (cement grout, 1.6 kg/L, no waste)
| Tile size | Thickness | 1/16 in joint | 1/8 in joint | 1/4 in joint |
|---|---|---|---|---|
| 2 × 2 in mosaic | 1/4 in | 13.0 lb | 26.0 lb | 52.0 lb |
| 4 × 4 in | 1/4 in | 6.5 lb | 13.0 lb | 26.0 lb |
| 3 × 6 in subway | 5/16 in | 8.1 lb | 16.3 lb | 32.5 lb |
| 6 × 6 in | 5/16 in | 5.4 lb | 10.8 lb | 21.7 lb |
| 12 × 12 in | 3/8 in | 3.3 lb | 6.5 lb | 13.0 lb |
| 12 × 24 in | 3/8 in | 2.4 lb | 4.9 lb | 9.8 lb |
| 24 × 24 in | 3/8 in | 1.6 lb | 3.3 lb | 6.5 lb |
Values are approximate; actual use depends on how full the joints are packed, the thin-set squeezing into the joints and the product. Always buy a little extra from the same batch so the color matches.
Frequently asked questions
How do I calculate how much grout I need?
Use the formula kg per m² = (A + B) ÷ (A × B) × C × D × density, where A and B are the tile length and width in mm, C is the joint width in mm, D is the joint depth in mm and density is about 1.6 kg/L. Multiply by the area in m² and add 10% for waste.
How much grout do I need for 100 square feet?
It depends mostly on tile size and joint width. For 12 × 12 in tiles 3/8 in thick with 1/8 in joints, you need about 6.5 lb of grout per 100 sq ft, so a 25 lb bag covers roughly 380 sq ft. With 3 × 6 in subway tiles 5/16 in thick and 1/16 in joints you need about 8 lb per 100 sq ft, because the narrow joints are offset by many more of them.
Why do small tiles need more grout?
Smaller tiles have many more joints per square foot. 2 × 2 in mosaics have six times as much joint length as 12 × 12 in tiles, so they use several times more grout for the same area and joint width.
Should I use sanded or unsanded grout?
Unsanded grout is generally used for joints of 1/8 in (3 mm) or less, and sanded grout for wider joints, because the sand stops wide joints from shrinking and cracking. Always follow the grout manufacturer's joint width range.
Is the joint depth the same as the tile thickness?
Usually, yes. Grout fills the joint from the thin-set to the tile surface, so the depth is the tile thickness minus any thin-set that squeezes up into the joint. Using the full tile thickness gives a slightly generous estimate.
What grout density should I use?
Most cement-based grouts have a density around 1.6 to 1.9 kg/L once mixed. Epoxy grouts are similar. The product's technical data sheet often lists coverage or density; 1.6 kg/L is a common value used by grout manufacturers in their coverage formulas.