How to measure the square footage of a room

What you need

A tape measure (or a laser measure), a pencil and paper, and a calculator. Our free square footage calculator does the maths for you, including L-shaped rooms.

Measuring a rectangular room

1. Measure the length: along one wall, from corner to corner at floor level.
2. Measure the width: along the wall at right angles to it.
3. Write both down in feet. If you measured in feet and inches, turn the inches into a fraction of a foot by dividing by 12. Nine inches is 0.75 ft, so 11 ft 9 in is 11.75 ft.
4. Multiply length by width. That’s the floor area in square feet.

Worked example: a bedroom 13 ft 6 in by 11 ft is 13.5 × 11 = 148.5 sq ft.

Measuring an L-shaped room

An L-shaped room is two rectangles joined together.

1. Sketch the room and draw one line that splits it into two rectangles.
2. Measure both sides of each rectangle.
3. Work out each area and add them together.

Worked example: a living room made of a 16 × 12 ft main area and an 8 × 6 ft dining nook is 192 + 48 = 240 sq ft.

You can also work it the other way round: measure the whole outer rectangle, then subtract the corner that isn’t part of the room. The calculator has a “subtract a cut-out” button for exactly this.

Converting to square metres or square yards

• Square metres: multiply square feet by 0.09290304. That figure is exact: a foot is defined as 0.3048 metres, so a square foot is 0.3048 × 0.3048 m² (NIST).
• Square yards: divide square feet by 9.
• Back to square feet from square metres: divide by 0.09290304, or multiply by about 10.764.

Measuring with your iPhone

If you don’t have a tape measure to hand, a measuring app can give you a quick estimate. In The Measure App, the Floor Plan tool lets you tap each corner where the walls meet the floor and walk around the room. It draws the plan with every wall length, the area and the perimeter, and handles L-shapes. The Area tool does the same for a single flat surface.

Camera measurements are estimates, though. For buying materials, check the key lengths with a tape measure. Our guide is the iPhone Measure app accurate? explains why.

Room area isn’t always “official” square footage

Adding up rooms gives you the floor area you can walk on. Official figures can follow different rules. The U.S. Census Bureau, for instance, counts finished floor area, leaves out garages and porches, and in concept measures to the outside of the exterior walls (U.S. Census Bureau). Appraisers working to Fannie Mae’s guide must use the ANSI square footage method (Fannie Mae Selling Guide B4-1.3-05). If a number matters for a sale, a mortgage or a contract, ask the professional handling it how they measure.