Running out of tiles mid-project is a common headache, and it is worse when the exact tile is out of stock by the time you reorder. A careful count before you buy, with the right waste allowance, avoids both problems.
How it works
The basic count is floor area divided by the area of one tile. Then add waste: 10 percent for a straight grid layout in a rectangular room, 15 percent for a brick or staggered pattern, and 20 percent for diagonal or herringbone layouts, which create many angled cuts. Round up to whole boxes, because tiles are sold by the box, and keep at least one spare box for future repairs.
Step by step
- Measure the floor length and width and multiply to get the area in square feet.
- Subtract large permanent fixtures only if they sit on the floor and will not be tiled under, such as a built-in bath plinth.
- Find the area of one tile in square feet: length times width in feet.
- Divide floor area by tile area to get the base tile count.
- Multiply by 1.10, 1.15, or 1.20 depending on your layout pattern.
- Divide by tiles per box, round up to whole boxes, and add one spare box.
Worked example
A bathroom floor is 8 feet by 6 feet = 48 square feet. Tiles are 12 by 12 inches, which is 1 square foot each, so the base count is 48 tiles. For a staggered brick pattern, add 15 percent: 48 x 1.15 = 55.2, so 56 tiles. If boxes hold 10 tiles, that is 6 boxes, plus 1 spare box = 7 boxes. For a diagonal layout on the same floor, 48 x 1.20 = 57.6, so 58 tiles, still 6 boxes plus spare.
Common mistakes
- Measuring in mixed units, such as inches for the room and feet for the tile, without converting.
- Using the same 10 percent waste for a diagonal layout, which needs far more cuts.
- Forgetting that tiles around a toilet flange and door frame create offcuts you cannot reuse.
- Skipping the spare box, then finding the tile discontinued when one cracks years later.
Try it with the free tool
You can follow every step above by hand, but the free tool below does the same calculation instantly. Try your own numbers in it, then check one result by hand so you trust the method as well as the answer. Open the full tool here: open the tool.
Checklist before you finish
- Write down every input number first, with its unit, before you calculate anything.
- Work through the steps in order, and do not skip the unit conversions.
- Check the answer against the worked example above: is it the right size, and does the direction make sense?
- Round only at the end, and keep the unrounded figure for any follow-up calculation.
Practice with your own numbers
Pick three cases of your own and work each one by hand. First, try a simple round-number case you can check mentally. Second, try a realistic case with awkward numbers, the kind you will actually meet. Third, try an edge case, such as a very small or very large input, and confirm the answer still behaves sensibly. If any case gives a surprising result, re-check the units and the formula step by step before you trust it.
If your answer looks wrong
Most errors come from a small set of causes. Check that you used the same units throughout, that you divided where the formula divides and multiplied where it multiplies, and that you applied any percentage as a decimal. Check the order of operations: powers and brackets come before multiplication and division, which come before addition and subtraction. Finally, test the method on the worked example in this guide. If your method reproduces the example answer, the method is right and the inputs deserve a second look.
Quick tips
Dry-lay one row across the room before you fix anything, so you can centre the pattern and avoid a thin sliver tile at one edge. Check the shade batch number on every box; tiles from different batches can differ slightly in colour.