Calculate paint needed for walls based on room dimensions, doors, windows and number of coats.
What Is Paint Calculator?
A paint calculator estimates how much paint you need to cover a room or surface based on the dimensions. Paint coverage varies by brand and type, but most standard emulsion paints cover approximately 10–12 square metres per litre per coat. Without calculating, people frequently buy too much paint (wasting money) or too little (requiring an extra trip to the shop mid-project).
This tool calculates the total wall area, subtracts doors and windows, accounts for the number of coats needed and tells you exactly how many litres (and tins) to buy. It takes the guesswork out of decorating and helps you budget accurately.
How to Use This Tool
Enter the room dimensions: length, width and height of the walls.
Specify the number of doors and windows to subtract from the total area.
Select the number of coats (typically 2 for a colour change, 1 for a refresh).
Set the paint coverage rate if different from the default (check the tin label).
View the total area, litres needed and the number of standard tins to buy.
Tips & Best Practices
Always buy 10% more paint than calculated to account for touch-ups and uneven surfaces.
Two thin coats give a better finish than one thick coat and use roughly the same amount of paint.
Dark colours over light walls usually need a primer plus two topcoats — budget accordingly.
Textured walls (Artex, rough plaster) absorb more paint — increase the coverage estimate by 15–20%.
Common Use Cases
Calculating paint quantities before redecorating a room.
Budgeting for a whole-house painting project.
Comparing costs between standard and premium paint based on required quantities.
Avoiding waste by buying the right amount rather than guessing.
Frequently Asked Questions
How does it calculate paint needed?
Wall area minus doors/windows, multiplied by coats, divided by paint coverage (m² per litre). Standard coverage is 12m²/litre.