Work out how much paint you need

Measure your room, work out wall and ceiling area, then use the tin's coverage rate to calculate how much paint to buy.

AB-01Gather your tools and paperworkGet a tape measure, a notebook or your phone's notes app, and a calculator. If you already know the paint brand, find the tin or look up its coverage rate online before you start — it's usually printed as square metres per litre.

1 each · Tape measure (5m)

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1 each · Notebook and pen

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AB-02Measure each wallMeasure the length of each wall along the skirting, and the height from skirting to ceiling. Write each measurement down as you go, wall by wall, so you don't lose track in a bigger room. Round each figure up to the nearest 0.1m to keep the maths simple.

AB-03Measure the ceiling, if you're painting itMeasure the length and width of the room at floor level, then multiply the two figures to get the ceiling area. Ceilings often show flat colour more than walls and can need an extra coat, so keep this total separate from your wall figure.

AB-04Calculate the total paintable areaMultiply each wall's length by its height to get that wall's area, then add all the wall areas together for your total wall area. Do the same for the ceiling if you measured it. Keep wall and ceiling totals separate, since they're often different colours.

AB-05Subtract doors, windows and anything else you won't paintMeasure the height and width of each door and window, multiply to get its area, and subtract this from your wall total. A standard flush door is roughly 2000mm x 800mm (1.6m²), and a typical window opening is often around 1200mm x 1200mm (1.44m²) — always measure your own though. Don't bother subtracting small things like sockets or light switches, they make no real difference.

AB-06Check the coverage rate and work out litres neededLook on the tin, or the brand's website, for the coverage rate, usually shown as square metres per litre. This varies a lot: cheap emulsion might cover around 10m² per litre, while a good quality one-coat paint can cover 12-14m² per litre. Divide your total area by the coverage rate to find how many litres you need for one coat, then multiply by the number of coats — most walls need two, and a big colour change (especially to or from a dark shade) often needs three.

AB-07Buy with a margin and record your numbersRound your total litres up to the nearest tin size and add roughly 10% extra for touch-ups, patching or spills. Tins usually come in 2.5L, 5L and 10L sizes, so check which combination gets you closest without much leftover. Write the exact colour name, code and brand in your notebook or phone, so you can match it precisely if you need more later.

1 each · Emulsion paint, 2.5L tin

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1 each · Emulsion paint, 5L tin

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