Step by step
- Measure each wall’s length along the floor and add them to get the perimeter (or length + width, doubled, for a rectangle).
- Measure the wall height from floor to ceiling.
- Multiply perimeter by height for the gross wall area.
- Measure doors and windows (width × height) and subtract them. Standard sizes are about 20 and 15 sq ft.
- For the ceiling, multiply length by width.
Irregular rooms
Measure each wall separately in the wall paint calculator, or find an odd floor area with the square footage calculator. Vaulted ceilings: measure the rise and use the ceiling calculator.
Measuring tips
- Round up to the next half foot.
- Measure twice. Corners and baseboards can make walls look different lengths.
- Do not forget closets: add each as another room.
Estimates only. Check your paint can’s label for coverage. Prices are typical 2026 US figures; use your store’s.