How do you calculate wall square footage for paint?

Multiply the total length of the walls (the room's perimeter) by the ceiling height to get gross area, then subtract the area of any doors and windows. That net figure is what you buy paint against, typically with 10% added for waste.

Do you subtract doors and windows from wall square footage?

Yes — you don't paint, paper, or drywall over a door or window opening, so subtracting their combined area gives a more accurate material estimate than using the gross wall area alone.

Do Canadian painters quote by square foot of wall or by room?

Most Canadian painting contractors quote per square foot of net wall area (after subtracting doors and windows), though some give a flat per-room price for standard-sized rooms. Getting the net square footage first, as this calculator does, makes it easy to sanity-check either kind of quote.

Wall Square Footage Calculator — Wall Area for Paint & Wallpaper

How to Calculate Wall Square Footage

Wall square footage is the paintable or coverable area of a room's walls — not just the floor area, but the actual vertical surface you'd cover with paint, wallpaper, or drywall. It's the total wall length (the room's perimeter) multiplied by the ceiling height, minus the area taken up by doors and windows, since you don't paint or paper over those. This calculator does that subtraction for you: enter your wall lengths and ceiling height, add how many doors and windows you have, and get a net square footage you can actually order materials against.

How to Use the Wall Square Footage Calculator

Pick the room shape: rectangle (enter two wall lengths), square (enter one length), or "other" if you'd rather enter the total wall length directly.
Enter the ceiling height — this is the same for every wall in a standard room.
Enter the number of doors and windows. Each comes with a standard average area already filled in, but you can override it if yours are a different size.
Read off the net wall area, add a waste allowance if you like, and see a rough material cost estimate for your country.

The Wall Square Footage Formula

Gross wall area = total wall length × ceiling height. For a rectangular room, total wall length is 2 × (length + width) — the room's perimeter. Then subtract the door and window openings: net wall area = gross area − (door area × door count) − (window area × window count).

Worked example: a 12 ft × 10 ft room with an 8 ft ceiling has a perimeter of 2 × (12 + 10) = 44 ft, so gross wall area = 44 × 8 = 352 sq ft. Subtract one standard door (≈21 sq ft) and one standard window (≈12 sq ft): 352 − 21 − 12 = 319 sq ft of net paintable wall.

Pro Tips

Add 10% for waste on paint or wallpaper to cover cutting, trim losses, and touch-ups — this calculator's waste field does that automatically. If your doors or windows are noticeably larger or smaller than average (a patio door, a bay window), override the per-opening area rather than relying on the defaults.

For the 319 sq ft worked example above, at a typical Canadian rate of about CAD 3.20 per sq ft for paint plus two-coat labor, that comes to roughly CAD 1,020 for the room.