Wall Square Footage Calculator
Find the paintable wall area of a room, minus doors and windows, plus the paint you will need.
🧱 What is the Wall Square Footage Calculator?
The wall square footage calculator works out how much wall area you actually need to paint or cover in a room. It takes the room's length, width, and ceiling height to find the total wall area, then subtracts the doors and windows to give the net paintable square footage, and estimates the gallons of paint required.
Anyone decorating a room needs this figure. Buy paint from the gross wall area and you overspend and end up with half-used tins; ignore the openings and you still overspend. The net area is what determines how much paint, wallpaper, or drywall you buy. Homeowners planning a repaint, renters skimming a feature wall, and contractors quoting a job all start by turning room dimensions into paintable area.
The method is perimeter times height, minus openings. The perimeter of a rectangular room is twice the length plus the width, and multiplying by the ceiling height gives the gross wall area of all four walls. From that you subtract a realistic allowance for each door, about 21 square feet, and each window, about 15 square feet, though you can enter your own sizes. Dividing the net area by paint coverage, typically 350 square feet per gallon per coat, gives the quantity to buy.
This tool is useful because it captures the details that catch people out: the doubling of walls, the subtraction of openings, the number of coats, and the conversion to gallons. You enter the room and its openings and instantly get gross area, opening area, net area, and paint needed, with the working shown so nothing is a mystery.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - Bedroom, 12 by 10 feet
Example 2 - Living room, 20 by 15 feet
Example 3 - Small room, 10 by 10 feet
❓ Frequently Asked Questions
🔗 Related Calculators
How do you calculate wall square footage?
Multiply the room perimeter by the ceiling height, then subtract the doors and windows. The perimeter is 2 times length plus width. For a 12 by 10 foot room with 8 foot ceilings, gross area is 2 x (12 + 10) x 8 = 352 square feet, minus openings for the net paintable area.
How much wall area does a door or window take up?
A standard interior door is about 21 square feet (3 feet wide by 7 feet tall) and an average window is about 15 square feet, though sizes vary. Subtract the actual area of each opening from the gross wall area. This calculator uses those defaults, which you can change.
How much paint do I need for a room?
Divide the net wall area by the paint coverage, about 350 square feet per US gallon per coat, then multiply by the number of coats and round up. A room with 301 square feet of net wall needs one gallon for a single coat, or two gallons for two coats.
How do I calculate paintable area with doors and windows?
Start with the gross wall area (perimeter times height), then subtract the combined area of all doors and windows. For one door (21 square feet) and two windows (15 square feet each), subtract 21 + 30 = 51 square feet from the gross area to get the paintable net area.
Should I include the ceiling in wall square footage?
No, wall square footage covers only the vertical walls. If you are painting the ceiling too, calculate it separately as length times width, the same as floor area. This calculator focuses on the walls and their paint requirement.
How much does one gallon of paint cover?
About 350 square feet per coat on smooth, previously painted walls, though 250 to 400 is the typical range. Rough or porous surfaces cover less, and the first coat on bare drywall covers less than later coats. Plan on the lower end for a reliable estimate.
How do I find the wall area of an irregular room?
Break the room into rectangular sections, calculate the wall area of each using perimeter times height, and add them together, then subtract all openings. For an L-shaped room, treat it as two rectangles and be careful not to double-count the shared internal corner.
Do two coats need twice the paint?
Yes, roughly. Each coat covers the same net area, so two coats need about double the paint of one coat, though the second coat can sometimes go a little further on a sealed surface. This calculator multiplies the area by the number of coats you enter.