Paint Calculator

About Paint Calculator

Paint Calculator estimates how many litres and gallons of paint are needed to cover the walls of a room. Enter the room length, width, and wall height, then subtract doors (1.8 m² each) and windows (1.0 m² each). Adjust the coverage rate to match your paint brand (default 10 m²/L) and choose 1, 2, or 3 coats. Results are shown in both metric and imperial. Standard interior latex paint covers approximately 10 to 12 m² per litre on a prepared surface. The calculator lets you adjust this coverage rate to match the exact spread rate printed on your paint tin. Results are shown in both metric (litres) and imperial (gallons) so you can shop in either unit system.

How to use Paint Calculator

  1. Enter room length, width, and wall height in metres
  2. Set the number of doors and windows to subtract their area
  3. Choose number of coats and see litres and gallons needed

Frequently Asked Questions

How is the paint amount calculated?
The calculator computes total wall area (2 x (length + width) x height), subtracts door and window areas, then divides by the coverage rate and multiplies by the number of coats.
What is the default coverage rate?
The default is 10 m² per litre, which is typical for standard interior latex paint. Premium or thicker paints may cover 8-12 m²/L. Check your paint tin for the exact spread rate.
How many litres of paint do I need for a 12x12 room?
A 3.6 m x 3.6 m room with 2.4 m ceilings has approximately 35 m² of wall area after subtracting a door and window. At 10 m²/L with two coats, you need about 7 litres. Use the calculator to enter your exact dimensions and subtract your specific openings.
Should I use one coat or two?
Two coats are recommended for most paint jobs, especially when changing colour or covering a dark shade. One coat may be enough for touch-ups on a matching colour or when using a paint-and-primer product. The calculator supports 1 to 3 coats.
Can I adjust the coverage rate?
Yes. The coverage rate field defaults to 10 m²/L but can be changed to match the exact spread rate on your paint tin. Premium or high-coverage paints may state 12 m²/L; thicker masonry paints may only cover 6-8 m²/L.
Is Paint Calculator free and private?
Yes. Paint Calculator is completely free with no account required. All calculations run in your browser and nothing is uploaded or stored.
Does Paint Calculator work on mobile?
Yes. Paint Calculator is fully responsive and works in all modern browsers on desktop, mobile, and tablet.

Related Tools