Paint Calculator
Size up a room’s paint from its perimeter and ceiling height, minus doors and windows, across your coats — in litres and gallons, and built to handle tall loft walls.
Paint needed
Wall area is your 20 m perimeter × 3 m ceiling (60m²), less a standard allowance for 1 door(s) and 2 window(s), covered 2 time(s) at ~10 m² per litre. Buy a little extra for touch-ups and porous surfaces.
Buy once, not twice
Under-buy and you’re back at the shop mid-job hoping the next tin matches the batch; over-buy and half-used cans stack up in the cupboard. Estimating from the actual wall area — perimeter times ceiling height, less the doors and windows — gets you close enough to buy with confidence.
Lofts make the ceiling-height factor impossible to ignore. A tall wall is a lot more paint than the floor plan hints at, so this calculator asks for height directly and multiplies the area, coats, and coverage to land on a litre and gallon figure you can take to the counter.
Frequently Asked Questions
How much paint do I need for a room?
Work out the wall area — perimeter times ceiling height — subtract the doors and windows you won't paint, then multiply by the number of coats and divide by the paint's coverage (about 10 m² per litre). For a 20 m room at 3 m high with two coats, that's roughly 11 litres before openings are removed.
Why does ceiling height matter so much in a loft?
Wall area is perimeter × height, so a tall loft ceiling multiplies the paintable area directly. A 4 m ceiling needs a third more paint than a standard 3 m one for the same floor plan — which is exactly why estimating from floor area alone comes up short.
What coverage should I assume?
This calculator uses about 10 m² per litre per coat, a common figure for emulsion on a smooth, sealed wall. Rough plaster, bare drywall, or a strong colour change soak up more, so treat the result as a floor and buy a little extra.
How many coats should I plan for?
Two coats is the usual default and what the calculator assumes. A dramatic colour change, patchy old paint, or fresh filler often needs a primer or a third coat — bump the coats figure up and the estimate scales with it.
Does it account for doors and windows?
Yes — each door removes about 1.8 m² and each window about 1.5 m² from the wall area, since you're not painting those. Enter how many the room has and the paintable area drops accordingly.
Estimates for planning — not professional real-estate, architecture, or financial advice. Always check the coverage stated on the tin and buy a little extra for touch-ups.