Interior & Finishing Calculators

Why square footage comes first

Almost every interior material is sold by coverage, so the room's area is the number that drives all of it. Get it right once and paint, flooring, tile and underlay all fall out of it. The common mistakes are measuring the outside of the room instead of the finished inside face, forgetting alcoves and bay windows, and rounding each wall down. Measure to the nearest inch, add the sections separately rather than averaging, and let the calculator do the conversion.

Waste allowances are not padding

Every material here is cut to fit, and the offcuts are rarely reusable. Ten percent is the normal allowance for tile and flooring in a simple rectangular room; fifteen for diagonal or herringbone layouts, and for rooms with lots of jogs, doorways and islands. Plank flooring also needs enough spare for the first and last row to be a sensible width. Buying from the same batch matters too — tile and laminate shade varies between production runs, so a top-up box bought three weeks later may not match.