Paint & Wallpaper Calculators

How paint & wallpaper estimating works

Paint and wallpaper are both estimated from wall area, but they are bought very differently. Paint is a liquid sold in fixed tin sizes, so the job is to find the smallest combination of gallons and quarts (or 5 L, 2.5 L and 1 L tins) that covers your area for the number of coats you need. Wallpaper is sold in rolls of fixed width and length, and because you hang it in full-height drops, the real constraint is how many drops you can cut from each roll once the pattern repeat is taken into account.

Coverage per coat varies far more between paints than most people expect — from about 250 to 400 sq ft per gallon (6–10 m² per litre) for interior emulsion. Always use the figure on your tin when you have it. For wallpaper, check the batch number on every roll and buy one spare.

Glossary

Emulsion (UK) / latex (US)

water-based wall paint

Coverage

area one unit covers per coat

Drop

one full-height strip of wallpaper

Pattern repeat

vertical distance before the design repeats

Updated 2026-10-18 by the DIYCalcLab Editorial Team · How we calculate