Paint Calculator
Enter your wall dimensions and paint coverage to see exactly how much paint to buy, including doors, windows, and extra coats.
How to use the paint calculator
- Choose metric or imperial units.
- Enter the total wall length and wall height (or add walls one at a time).
- Subtract the area of doors and windows.
- Enter your paint's coverage rate and the number of coats you plan to apply.
- The amount of paint needed updates live as you adjust any value.
How it works
Wall area is calculated as Perimeter × Height, then door and window area is subtracted to get the net paintable area: Net area = (Perimeter × Height) − Openings. That figure is multiplied by the number of coats and divided by your paint's coverage rate to get the volume required: Paint needed = (Net area × Coats) ÷ Coverage per litre (or gallon).
Examples
| Input | Result |
|---|---|
| 14 m wall perimeter, 2.4 m height, 3 m² openings, 2 coats, 10 m²/L coverage | ≈ 6.1 litres |
| 48 ft wall perimeter, 8 ft height, 20 ft² openings, 2 coats, 350 ft²/gal coverage | ≈ 2.1 gallons |
Frequently asked questions
How many coats of paint do I actually need?
Two coats is standard for a color change or new drywall. One coat can work for a refresh in the same color; three coats may be needed for very dark-to-light transitions.
Do I need to subtract doors and windows?
Yes — leaving them in your measurement will overestimate paint needed, sometimes by 10–15% in rooms with lots of glazing.
What paint coverage rate should I use?
Check the tin — most interior emulsion covers 10–12 m² per litre (350–400 ft² per gallon), but textured or very absorbent walls will cover less.
Should I paint the ceiling too?
Add the ceiling as a separate area (Length × Width) at one coat, since ceilings usually need less coverage than accent walls.
How much extra paint should I buy for touch-ups?
Round up to the next full can and keep a small labeled leftover for future touch-ups — paint color batches can vary slightly over time.