How to use
Enter the room size and the total area of windows and doors — they don’t get painted. Choose walls, ceiling or both, then enter the number of coats, the coverage from the can and the can size. You’ll see how much paint you need and how many cans to buy. Prefer meters and liters? Switch the units above the form.
How it’s calculated
- Wall area = room perimeter × ceiling height − openings: 2 × (length + width) × height − windows and doors.
- Ceiling area = length × width.
- Paint = area × coats ÷ coverage.
- Cans are rounded up — you can’t buy part of a can.
A quick rule for openings: about 21 sq ft for a standard door (3 × 7 ft) and 15 sq ft for an average window (3 × 5 ft).
Where to find the coverage
It’s on the label, usually as “covers 350–400 sq ft per gallon” — enter that number as is. If the label gives coverage per quart, multiply by 4 to get sq ft per gallon. The default, 350 sq ft/gal, is a typical figure for interior latex paint on smooth, primed walls with a little margin. Textured, porous or unprimed surfaces (new drywall, fresh plaster) take more paint — lower the coverage.
Examples
- A 16 × 13 ft room with 8 ft ceilings, one door and one window (36 sq ft), two coats: 428 sq ft of wall, 2.4 gallons of paint — buy 3 gallons.
- The same room with the ceiling: 636 sq ft, 3.6 gallons, so 4 gallons.
- Just the 16 × 13 ft ceiling, two coats: 1.2 gallons.
FAQ
How many coats do I need? Usually two. One may be enough when repainting a similar color with a high-hide paint; a dramatic color change can take three.
Is primer included? No — primer is calculated separately using its own coverage. A well-primed wall soaks up less paint.
Should I buy extra? A little left over is handy for touch-ups, and paint from the same batch matches exactly. The calculator already rounds cans up.
Hanging wallpaper instead? Use the wallpaper calculator.