Paint coverage calculator
Area, coats and surface type, converted to litres and tins to buy — rougher surfaces eat more paint than the tin's headline figure suggests.
Wall & paint detail
Total wall or ceiling area — deduct large openings first.
Two coats is standard for an even, opaque finish.
Paint to buy
— rounds up to 4 tins to buy.
Estimate only — check the tin. Excludes a separate mist coat on bare plaster. Coverage rates vary by product — confirm against the specific paint's data sheet.
The coverage figure on a paint tin is a best case, tested on a smooth, primed surface under ideal conditions. Real walls rarely match that — and surface type is the single biggest variable most people underestimate when working out how much to buy. Get it wrong and it's either a wasted trip to the merchant mid-job or paint left over that never gets used.
Why surface type changes everything
A smooth, previously painted or well-skimmed plaster wall lets paint spread a long way, since there's little for it to soak into — commonly 12m² or more per litre, per coat. Standard surfaces that have been painted before but have some texture or minor wear sit lower, around 10m² per litre. Bare plaster, masonry and heavily textured surfaces are far more absorbent and can drop to 6m² per litre or less, especially on the first coat, because a good chunk of that first litre simply disappears into the surface rather than sitting on top of it.
Coats matter more than the maths suggests
Two coats isn't just about colour depth — it's what makes coverage even across a wall that's absorbed paint unevenly. New or bare plaster is usually mist-coated first: paint thinned with water, which doesn't follow the same coverage rate as the finish coats that follow and is worth budgeting for separately rather than folding into this calculation.
A worked example
A 40m² wall area, two coats, on a standard surface rated at 10m² per litre: (40 × 2) ÷ 10 = 8 litres. Buying in 2.5L tins, that rounds up to four tins — 10 litres bought against 8 needed, which is a sensible margin for touch-ups and second-coat variation rather than cutting it exactly to the litre.
What this isn't
This doesn't deduct window and door openings from the area, doesn't account for a separate mist coat on bare plaster, and doesn't replace the specific product's own coverage claim — different paints, even within the same surface category, can vary significantly. Check the tin or data sheet for the actual coverage rate before finalising a large order.
Seen enough? Claim your patch.
TradesInvo captures every enquiry, replies first, and runs it to a booked, quoted, paid job. Early access is five founder slots per postcode — check yours.