How to Use the Paint Coverage Calculator
- Enter the total wall width and height, or room dimensions.
- Subtract the area of doors and windows.
- Set the number of coats and paint coverage rate.
- See the paintable area and how much paint to buy.
How much paint do I need?
To work out how much paint you need, calculate your total wall area, subtract doors and windows, multiply by the number of coats, and divide by your paint's coverage rate. As a rough guide, one litre of paint covers about 10–12 m², and one US gallon covers roughly 350–400 sq ft, for a single coat on a smooth surface.
Most walls need two coats — especially over a new, patched, or contrasting colour — so remember to double the area. The calculator above does all of this for you: enter your wall area, deduct openings, choose your coats and coverage rate, and it tells you exactly how many litres or gallons to buy.
Tips for an accurate paint estimate
Coverage varies a lot by surface and paint type. Rough, porous, or previously-unpainted surfaces (bare plaster, brick, render) soak up more paint, so use the lower end of the coverage range. Primer or a first coat over a dark colour also reduces coverage.
Always round up and buy a little extra for touch-ups and future repairs — running out mid-job and getting a slightly different batch is a common frustration. Check the coverage figure printed on your specific paint tin and enter that into the calculator for the most accurate result.
Frequently Asked Questions
How much does one litre or gallon cover?
Typically about 10-12 square metres per litre (roughly 350-400 sq ft per gallon) for one coat on a smooth surface. The calculator lets you set the coverage rate from your paint's label.
Should I add extra for a second coat?
Yes. Most walls need two coats, especially over a new or contrasting color. Set the number of coats and the calculator multiplies accordingly.
Does it account for doors and windows?
Yes. Subtract their total area so you don't overestimate the paint you need.