Paint Calculator
Enter your room size, subtract doors and windows, and get how much paint to buy for the number of coats you plan.
How we calculate
We measure the wall area from your perimeter and height, subtract about 20 ft² (1.9 m²) per door and 15 ft² (1.4 m²) per window, add the ceiling if you asked for it, multiply by the number of coats, then divide by a coverage of 350 ft² per US gallon (8.6 m² per litre). Tin counts are rounded up.
Tip: Bare plaster, filler patches and strong existing colours drink paint — allow an extra primer coat rather than stretching your topcoat.
Assumptions & things to watch
- Assumes coverage of about 350 ft² per US gallon (roughly 8.6 m² per litre) on smooth, primed surfaces.
- Rough, porous or strongly coloured walls can cut coverage by 20–30% and may need a primer coat.
- Buy paint in one batch where possible so the colour matches across tins.
Estimates only — always double-check quantities with your supplier before ordering.
Quick tips: Paint
How much paint do I need for one room?
A typical 12 × 10 ft room with 8 ft ceilings needs roughly 2 US gallons (about 7.5 litres) for two coats on the walls, before any ceiling paint.
How many coats of paint do I need?
Two coats is standard. Go to three when covering a dark colour with a light one, or use a tinted primer first to save a topcoat.
How much does a gallon of paint cover?
About 350 sq ft (33 m²) per coat on a smooth, sealed surface. Textured, porous or fresh plaster walls can drop that to 250 sq ft.
Should I paint the ceiling too?
If you're changing the wall colour, painting the ceiling first avoids cutting-in twice. Use a dedicated flat ceiling paint — it hides imperfections better.
Do I need primer?
Yes on bare plaster, wood, filler patches, or when going from a dark to a light colour. Over sound, previously painted walls in a similar shade you can usually skip it.