How do you include grout joints in a tile layout?
Count the actual tile dimensions and the gaps between them. For example, a row of 10 tiles has 9 joints between the tiles. Count gaps against the walls separately. The size shown on the box may not be exact enough.
Explanation
Measure the tiles you will use
A tile sold as 600 × 600 mm may not measure exactly 600 mm on each side. Measure several tiles or ask the supplier to confirm their actual size. For rectangular tiles, check both length and width.
A small difference repeated along a row can move the cuts at the wall. That is why the plan needs the actual product dimensions.
Count the gaps as well as the tiles
A grout joint is the gap between two tiles, which will be filled later. Picture three tiles side by side: there are two gaps between them. Ten tiles have nine gaps.
Add the width of those joints to the tile widths. Use the same unit throughout the calculation, such as millimetres. 60 cm = 600 mm, while 3 mm = 0.3 cm. In the planner, check the unit shown beside each field.
Keep gaps against the walls separate
These are not extra joints between tiles. If you have already subtracted them from the available width, do not subtract them again.
Ask the supplier or tiler which widths your project needs. Do not change the joints simply to force a row to fit.
Enter these measurements in the tile layout planner, then check the edge cuts. The beginner’s guide explains how to choose a starting point.
Formula / method
Row length = total tile width + total joint width.
Multiply the actual width of one tile by the number of tiles. Then add the width of one joint multiplied by the number of gaps between them. A row of full tiles has one fewer internal joint than tiles. This calculation excludes cut pieces at the ends and gaps against the walls.
Concrete example
Example: you have 10 tiles, each 598 mm wide, with 3 mm joints.
The tiles take up 10 × 598 = 5,980 mm. The 9 joints add 9 × 3 = 27 mm. The row is therefore 6,007 mm, or 6.007 m, without the gaps against the walls.
Using only ten nominal 600 mm widths would give 6,000 mm. Using 600 mm for each tile and adding the joints would give 6,027 mm. This is why both measurements matter. The 3 mm joint is an example, not an installation instruction.
Common mistake
Do not use one joint width for every job: it depends on the tiles and installation. A precise result on screen does not guarantee that the delivered tiles or walls will exactly match the measurements entered.
Sources & methodology
Features: Outilo tile layout planner, checked on 3 October 2026. The formula counts spaces in a straight row. Calculations and the worked example are original and do not prescribe a grout joint width.
This content follows Outilo's editorial guidelines.