Project Parameters
Subtract the combined area of openings from the wall area.
Instant Estimate
Room Perimeter
Paintable Wall Area
After subtracting doors and windows.
Gross Wall Area
Metric Floor Area
Estimates use standard building formulas. Verify with an on-site contractor.
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Guide
How to calculate the square footage of a room
A single set of room measurements can answer several different project questions. Floor and ceiling area use length × width, while wall projects use perimeter × wall height.
Measure length and width
Measure finished wall to finished wall at floor level. For irregular rooms, split the floor into rectangles and add their areas.
Measure wall height
Measure from the finished floor to the ceiling. Use an average height for sloped ceilings.
Subtract openings
Add the area of doors and windows only when estimating wall finishes such as paint or wallpaper.
Mathematics
Formulas used
Floor and Ceiling Area
Length × WidthThe horizontal area used for flooring, rugs, ceilings, and lighting.
Wall Area
2 × (Length + Width) × Height − OpeningsThe paintable or finishable area of all four walls.
Answers & FAQ
Frequently asked questions
How many square feet is a 12 by 12 room?▼
A 12 ft by 12 ft room has 144 square feet of floor and ceiling area.
Are wall square feet the same as floor square feet?▼
No. Floor area is length times width. Wall area depends on the room perimeter and wall height, minus openings.
How do I calculate an L-shaped room?▼
Divide the room into two rectangles, calculate each rectangle's area, and add the results.
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