How much extra tile should I order?

10% for a straight lay in a simple rectangular room, 15% for a diagonal lay, and up to 20% for rooms with lots of cuts. Consider one extra box beyond that for future repairs.

How much thinset do I need?

A 50 lb bag covers roughly 80 square feet with a 1/4 inch square-notch trowel. Larger tiles need a bigger notch and cover less — a 1/2 inch notch drops coverage to around 40 square feet per bag.

Tile and Flooring Calculator

Turn room dimensions into boxes of tile or flooring, including a waste allowance for cuts.

Draft — figures checked, awaiting an editorial read. Not indexed.

Boxes to buy— boxes

Floor area: — ft²
Area including waste: — ft²
Thinset (50 lb bags)Tile only — about 80 ft² per bag at a 1/4 in notch.: — bags

Formula: Area = length × width. Boxes = area × (1 + waste) ÷ coverage per box, rounded up.

What this calculates

This converts a floor area into whole boxes of tile, laminate, vinyl plank or engineered wood, with a waste allowance built in. Flooring is always sold by the box and boxes are never a round number of square feet, so the useful answer is never the area — it is how many boxes to put in the cart. There is also a strong argument for buying one box beyond the calculated number and keeping it: dye lots and production runs change, and a box of the same product bought two years later frequently does not match.

How it works

Floor area is length times width. The waste allowance is added as a percentage, and the result is divided by the coverage printed on the box, rounded up to a whole box. The waste percentage is doing more work here than in most calculators, because tile waste depends almost entirely on layout rather than on room size: a straight lay in a square room genuinely wastes about 10%, a 45-degree diagonal lay wastes 15% because every perimeter tile is cut on an angle, and a room with alcoves, an island or a hearth can reach 20%.

Worked example

A 12 by 10 foot kitchen using tile that covers 15 square feet per box, laid straight. Area is 120 square feet. With 10% waste that becomes 132. Divided by 15 that is 8.8 boxes, so you buy 9 — which gives you 135 square feet of tile and a few spares. For thinset, 120 square feet ÷ 80 square feet per bag is 1.5, so two 50 lb bags.

Common mistakes

Calculating the area and buying exactly that many square feet, with no allowance for the fact that every tile at the wall gets cut. Second, using a 10% allowance for a diagonal layout — the geometry of a diagonal lay wastes noticeably more, and the shortfall shows up right at the end of the job. Third, ordering boxes from two different lot numbers: check that they match before leaving the shop, because slight colour variation between lots is visible across a finished floor.

Common questions

How much extra tile should I order?: 10% for a straight lay in a simple rectangular room, 15% for a diagonal lay, and up to 20% for rooms with lots of cuts. Consider one extra box beyond that for future repairs.
How much thinset do I need?: A 50 lb bag covers roughly 80 square feet with a 1/4 inch square-notch trowel. Larger tiles need a bigger notch and cover less — a 1/2 inch notch drops coverage to around 40 square feet per bag.