How to Calculate Square Footage for Floors, Walls and Rooms

Basic square footage formula

For a rectangular area, multiply the length by the width. Both dimensions should be expressed in feet.

Square feet = Length × Width

Example: rectangular room

A room measuring 20 feet long and 12 feet wide has an area of 240 square feet.

20 ft × 12 ft = 240 ft²

How to measure multiple rooms

Calculate each room separately and add the individual areas together. This is usually more reliable than trying to treat an irregular floor plan as one large rectangle.

How to handle irregular spaces

Split the space into rectangles or other simple shapes.
Calculate each section separately.
Add the areas together.
Measure alcoves, extensions and offsets independently.

Square footage for walls

Wall area is calculated using wall length multiplied by wall height. If several walls have different dimensions, calculate each separately.

Wall area = Wall length × Wall height

Should doors and windows be deducted?

For rough estimates, small openings are sometimes left in the total. For more precise paint, siding or finish estimates, the area of significant doors and windows can be subtracted.

Measurement accuracy

Use actual measured dimensions instead of nominal room sizes when purchasing materials. Small differences become significant across large areas.