Estimate grout from tile and joint dimensions
Grout quantity depends on how much joint lies within each square metre. Enter tile dimensions, joint width, filled depth and product factor, or use a manufacturer’s known kg/m² rate.
Back to calculator ↑Measure the tile, joint and surface
Enter net tiled area in m². The formula route needs tile width and length in millimetres, the planned joint width, and the depth actually filled with grout. Do not automatically use the tile’s full thickness if the filled joint is shallower. Confirm joint dimensions with the tiler.
Run separate estimates for different tile sizes, joint widths or grout products. Smaller tiles create more joint length per square metre; a wider or deeper joint also consumes more. Keep movement joints and perimeter gaps separate because they may need a flexible sealant rather than ordinary grout.
Choose formula or known rate
The formula route calculates kg/m² as (tile width + length) ÷ (width × length) × joint width × filled depth × product factor, with every dimension in millimetres. It then multiplies by net area, applies allowance once and rounds to whole bags. The factor reflects the grout product; 1.6 is an illustrative Mapei Ultracolor Plus figure.
If the product sheet already provides a kg/m² rate for your tile and joint size, select the known-rate path and enter it directly. The calculator then skips the geometry formula. Check that the quoted rate uses the same joint depth and product type.
A checkable worked example
For 300 × 300 mm tiles, a 3 mm joint, 6 mm filled depth and factor 1.6, the rate is (300 + 300) ÷ (300 × 300) × 3 × 6 × 1.6 = 0.192 kg/m². Across 20 m², base consumption is 3.84 kg. These are illustrative dimensions, not a recommendation for joint width or depth.
At 10% allowance, required grout is 3.84 × 1.10 = 4.224 kg. With 2 kg bags, ceil(4.224 ÷ 2) means three bags, or 6 kg bought. The 1.776 kg difference is a calculated surplus before site waste and cannot be assumed to remain usable.
Confirm product and joint type
Read the chosen grout’s technical sheet for permitted joint widths, substrate, wet-area use, colour and mixing method. A factor of 1.6 is a product example, not a universal density. A different grout may call for its own factor or a published consumption table.
Movement joints, wall perimeters and changes of plane may require an appropriate flexible sealant. Keep those joints out of a simple grout assumption and ask the installer about the assembly. Also verify when the tile adhesive permits grouting and how the surface will be cleaned.
Common questions
Can I enter centimetres in the formula fields?
No. All tile and joint dimensions in the formula path are millimetres; 30 cm is 300 mm.
Is the 1.6 factor universal?
No. It is an example for Mapei Ultracolor Plus; check the actual product factor or published rate.
Should I grout the perimeter joint?
Movement and perimeter joints may need a flexible material; confirm the assembly with the installer.
Sources and calculation guidance
Check these against your chosen product’s label and instructions.