How do I calculate the square footage of a wall?

Multiply the wall's length by its height. A 14 ft wall with an 8 ft ceiling is 112 square feet. For a whole room, add the lengths of all the walls (the perimeter) and multiply by the height, then subtract doors and windows.

How many square feet is a door?

A standard 3 ft by 6 ft 8 in door is exactly 20 square feet. Estimators often use 21 square feet (3 by 7 ft) as a rule of thumb. A 2 ft 8 in door is about 18 square feet, and a 6 ft sliding patio door is about 40. Measuring the real openings gives the most accurate wall area.

Should I subtract windows from wall area?

For paint, wallpaper and tile, yes: you aren't covering the openings. A common allowance is 15 square feet per window, about a 3 by 5 ft window. For drywall, some estimators deduct only large openings, since the board is often hung over small windows and cut out afterward.

How do I find the wall area of a gable or vaulted wall?

Split it into a rectangle and a triangle. The rectangle is the wall's width times the height to where the slope starts. The triangle is the width times the extra rise to the peak, divided by 2. A 12 ft wide wall, 8 ft at the sides and 12 ft at the peak, is 96 + 24 = 120 square feet.

How do I calculate wall area for a whole house?

Add up each room's perimeter and multiply by the ceiling height, or do it room by room and add the results. Interior walls are counted on both sides this way, which is correct for paint and drywall, since both faces get covered. Then subtract the doors and windows.

Free calculator

Wall Square Footage Calculator (Minus Doors and Windows)

Free wall area calculator: perimeter times height, minus doors and windows, for one room or a whole floor.

Room length

Room width

Wall height

Floor to ceiling.

Doors

Each door

sq ft

3' × 7' allowance.

Windows

Each window

sq ft

3' × 5' allowance.

Result

Wall area, less openings

365sq ft

52.0 ft of wall × 8.0 ft high

Gross wall area: 416.0 sq ft
Doors (1): −21.0 sq ft
Windows (2): −30.0 sq ft

Wall by wall, before openings

Wall 1 (14.0 ft): 112.0 sq ft
Wall 2 (12.0 ft): 96.0 sq ft
Wall 3 (14.0 ft): 112.0 sq ft
Wall 4 (12.0 ft): 96.0 sq ft

Measure height from the floor to the ceiling. For paint, add the ceiling separately (length × width).

How it's calculated

Wall area = perimeter × wall height − doors − windows. A 14 × 12 ft room with 8 ft walls has a 52 ft perimeter: 52 × 8 = 416 sq ft, less one door (21 sq ft) and two windows (30 sq ft) = 365 sq ft.

How to use the wall area calculator

For a single room, enter its length, width and wall height. The calculator adds the four walls, shows each one, and subtracts the doors and windows. For several rooms or an odd-shaped space, switch to Total wall length and enter the sum of every wall you're covering. Opening sizes are editable: the defaults of 21 sq ft per door and 15 sq ft per window are allowances, so change them if you've measured your actual openings.

Gross wall area by room size and ceiling height

Before doors and windows:

Room	Perimeter	8 ft walls	9 ft walls	10 ft walls
10 × 10 ft	40 ft	320 sq ft	360 sq ft	400 sq ft
12 × 12 ft	48 ft	384 sq ft	432 sq ft	480 sq ft
12 × 14 ft	52 ft	416 sq ft	468 sq ft	520 sq ft
14 × 16 ft	60 ft	480 sq ft	540 sq ft	600 sq ft
15 × 20 ft	70 ft	560 sq ft	630 sq ft	700 sq ft

Opening sizes

Opening	Size	Area
Standard interior door	3' 0" × 6' 8"	20 sq ft
Narrow interior door	2' 8" × 6' 8"	17.8 sq ft
Rule-of-thumb door	3' × 7'	21 sq ft
Sliding patio door	6' 0" × 6' 8"	40 sq ft
Rule-of-thumb window	3' × 5'	15 sq ft

The rule-of-thumb sizes are slightly generous for a standard door, which leaves a small cushion when you buy paint. Big openings such as patio doors, picture windows and cased openings are worth measuring, since one of them can equal two or three standard windows.

Measuring walls accurately

Measure height from the finished floor to the ceiling, not to the top of the baseboard.
Rooms with two ceiling heights, such as a step-down room or a soffit, are easier as separate walls.
Stair walls and gable ends are a rectangle plus a triangle (width × rise ÷ 2).
Closets have their own walls: add their perimeters if they're being painted too.

What wall area is used for

Paint: wall area × coats ÷ coverage per gallon. The paint calculator does this room by room.
Drywall: wall area plus ceilings, plus waste, ÷ sheet size. See the drywall calculator.
Wallpaper and wall tile: the net area of just the walls being covered, plus the pattern repeat or cutting waste.

Measuring walls from a floor plan is faster than with a tape. FloorFigures is free: it traces each room on the plan and reports perimeter, wall area less openings, and ceiling area for every room.

Updated October 12, 2026 · FloorFigures

Questions

How do I calculate the square footage of a wall?: Multiply the wall's length by its height. A 14 ft wall with an 8 ft ceiling is 112 square feet. For a whole room, add the lengths of all the walls (the perimeter) and multiply by the height, then subtract doors and windows.
How many square feet is a door?: A standard 3 ft by 6 ft 8 in door is exactly 20 square feet. Estimators often use 21 square feet (3 by 7 ft) as a rule of thumb. A 2 ft 8 in door is about 18 square feet, and a 6 ft sliding patio door is about 40. Measuring the real openings gives the most accurate wall area.
Should I subtract windows from wall area?: For paint, wallpaper and tile, yes: you aren't covering the openings. A common allowance is 15 square feet per window, about a 3 by 5 ft window. For drywall, some estimators deduct only large openings, since the board is often hung over small windows and cut out afterward.
How do I find the wall area of a gable or vaulted wall?: Split it into a rectangle and a triangle. The rectangle is the wall's width times the height to where the slope starts. The triangle is the width times the extra rise to the peak, divided by 2. A 12 ft wide wall, 8 ft at the sides and 12 ft at the peak, is 96 + 24 = 120 square feet.
How do I calculate wall area for a whole house?: Add up each room's perimeter and multiply by the ceiling height, or do it room by room and add the results. Interior walls are counted on both sides this way, which is correct for paint and drywall, since both faces get covered. Then subtract the doors and windows.

Skip the typing. Measure the plan.

Open the floor plan in FloorFigures and every room is measured for you, with the same math per room. Try it free on a sample plan; nothing is uploaded.