For a rectangular area, multiply length by width. A room that measures 20 feet by 15 feet has 300 square feet of floor area.
Rectangle and square formulas
For rectangles, use length × width. For a square, multiply one side by itself. Use the Square Footage Calculator if you want the result converted automatically to square yards and acres.
How to calculate a circular area
Measure the diameter, divide it by two to get the radius, then use π × radius². Circular patios, fire-pit areas and landscape beds are common reasons to use this formula.
What about irregular rooms?
Break the floor or yard into simple shapes. Calculate each rectangle, square or circle separately, then add the areas. This makes your measurement easier to verify.
Why square footage matters
Flooring, paint, mulch, roofing and many other materials begin with area. After measuring, use the Flooring Cost Calculator or Mulch Calculator for the next step.