Wall lengths (leave any at 0 if you have fewer walls)
Doors and windows to deduct
Coverage
| Area | Amount |
|---|
Tins to buy
| Tin size | Tins needed | Total bought | Spare |
|---|
How this calculator works
Gross wall area is the sum of your wall lengths multiplied by the height, since every wall in a room shares the same ceiling height. Door and window areas are then subtracted at count × width × height each, using the standard UK internal door size of 1.98 × 0.76 m as the default, which you can change for taller doors or a non-standard opening. Litres needed is net area × coats ÷ coverage per litre, and the tins table just divides that litre figure by 1, 2.5 and 5 litre tin sizes, rounding up since part-tins aren't sold.
Picking a coverage figure
The 12 m2 per litre default is a reasonable mid-point for emulsion on a previously painted wall, but the tin in your hand is the better source: manufacturers print their own coverage rate, and it varies with the paint's finish (matt covers more thinly than a durable eggshell or a deep, saturated colour) and the surface underneath. Bare plaster, previously dark walls, or a colour change from dark to light all soak up more paint and may need a mist coat or an extra coat that this simple two-coat default doesn't include.
Choosing a tin size
Buying one larger tin is usually cheaper per litre than several smaller ones, but leaves more open paint to store or waste if you won't repaint soon; buying to the litre in smaller tins wastes less. The table above shows all three common sizes side by side with the spare litres each leaves, so you can weigh cost against leftover paint yourself.
What this calculator does not check
This tool covers wall paint only, not ceilings, skirting, or woodwork, each of which needs its own area and usually a different paint entirely. It doesn't account for a mist coat on new plaster, a stain-blocking primer on damp or nicotine-stained walls, or the extra coat that a dark-to-light colour change often needs. Treat the coats and coverage figures as your inputs to adjust, not fixed facts.
Related tools
Papering instead of painting? The wallpaper calculator works out roll count for the same walls, including the effect of a pattern repeat.