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Tile Calculator Guide
Tiles, boxes and grout — with the grout worked out from geometry rather than a chart, because grout depends far more on tile size than on floor size.
Grout fills the gap between tiles, so per square foot:
volume = 144 × thickness × [1 − (L×W) ÷ ((L+J)(W+J))]
A 4×4in tile needs 5.8× the grout of a 24×24in tile over the same floor — same area, same joint width.
Tile Size Drives Grout, Not Floor Size
This surprises people. Small tiles mean more joints per square foot, and grout volume tracks the total length of joint, not the area of floor.
A mosaic or a 3×6 subway wall will consume grout at a rate that makes no sense until you see it this way. Doubling the joint width roughly doubles the grout too — a 1/4in joint on 12×12 tile needs about twice what a 1/8in joint does.
Why This Page Won't Give You a Bag Count
The volume above is exact — it's geometry. Turning it into bags isn't, because it depends on the density of your specific product, and sanded, unsanded and epoxy grouts differ substantially.
Every manufacturer publishes their own coverage chart and they don't agree. So this gives you the exact volume and lets you enter your product's figure. If a calculator confidently tells you "buy two bags" without asking what grout you're using, it's guessing.
Waste Is About Pattern, Not Carelessness
A straight grid wastes about 10% — mostly the cuts at the perimeter. A diagonal layout wastes 15%, because every edge tile is cut on the bias and the offcut is a triangle that fits nowhere.
Herringbone wastes 20% or more for the same reason, doubled. That waste isn't optional and it isn't a sign you're bad at cutting; it's built into the pattern you chose.
Order the Whole Job, Check the Lot Number
Ceramic and porcelain are fired in lots and the colour shifts between them — sometimes subtly, sometimes not. The lot number is printed on the box.
Buy every box at once from the same lot, and buy a spare box beyond what this says. Tiles break during cutting, and finding a matching lot two months later is close to impossible if the line has moved on.
The Substrate Is the Job
Tile is rigid and unforgiving. A floor that flexes will crack the grout first and then the tile, and no amount of good tiling technique fixes a bouncy subfloor.
Check deflection before you start, use the right backer board, and in a wet area get the waterproofing right underneath. Tile is not waterproof — the assembly under it is.
Related: flooring calculator, paint calculator, square yards calculator.
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