How much paint for a room
Estimate liters or gallons of paint using wall area, number of coats and the coverage shown on the paint label.
For a rectangular room, start with the perimeter, multiply by wall height, subtract doors and windows, then divide by paint coverage. Multiply by the number of coats before dividing.
Liters = ((2 x (length + width) x height - openings) x coats) / coverage.
Worked example
A room measuring 4 m x 3 m with 2.4 m high walls has a perimeter of 14 m. Wall area is 14 x 2.4 = 33.6 m2. If doors and windows are 3 m2, paintable area is 30.6 m2. For two coats at 10 m2 per liter, you need 6.12 liters, or about 2 gallons.
Coverage assumptions
Many interior wall paints cover around 10 to 12 m2 per liter per coat on smooth surfaces. Rough plaster, dark color changes, new drywall or porous walls may require more paint and primer.
Common mistakes
- Using the floor area instead of wall area.
- Forgetting to multiply by the number of coats.
- Not deducting large doors and windows.
- Assuming every paint has the same coverage.
Use the calculator
Enter your room dimensions in the paint calculator. You can adjust coverage, coats and openings to match your project.
Frequently asked questions
How do I calculate paint for a room?
Use perimeter x wall height, subtract openings, multiply by coats and divide by coverage per liter.
How many square meters does one liter cover?
Many interior paints cover about 10 to 12 m2 per liter per coat on smooth surfaces. Check the label.
How many coats should I use?
Two coats are common for interior walls. More may be needed for dark colors, porous walls or new plaster.
This guide is for preliminary planning only. Product coverage, surface preparation, primer and application method can change the final quantity.