Estimate the liters or gallons of paint for a room, minus doors and windows, for any number of coats.
Paint needed
–
Wall area = 2 × (length + width) × height − doors − windows
Paint = area × coats ÷ coverage
A standard door is counted as about 1.9 m² (20 ft²) and a window as 1.5 m² (15 ft²).
Choosing colors? Try the color palette generator.
Work out the wall area: the perimeter (2 × length + 2 × width) times the height, minus doors and windows. Multiply by the number of coats and divide by the paint's coverage, usually about 10 m² per liter or 350–400 square feet per gallon.
Two coats give an even finish in most cases. One coat can be enough when repainting the same color with good paint; three may be needed for a big color change, such as light over dark.
Use primer on bare plaster or drywall, patched areas, stained walls, and when changing from dark to light. Primer is calculated the same way, usually with one coat.
Rough or textured walls absorb more paint, and rollers and trays hold some back. Buying about 10% extra, or one extra small can, is usually enough.