How to Measure an L-Shaped Room for Square Footage
A step-by-step method for measuring an L-shaped room accurately, including which dimensions to take and the subtraction formula that turns them into square footage.
An L-shaped room looks complicated to measure, but it's really just a rectangle with a smaller rectangle missing from one corner — once you see it that way, it only takes four measurements.
Step-by-step
- Measure the room's maximum length and maximum width as if the missing corner weren't there — this is your outer bounding rectangle.
- Measure the length and width of the missing corner (the notch) separately.
- Multiply each pair of measurements to get two areas: the outer rectangle and the cutout.
- Subtract the cutout area from the outer rectangle's area to get the true floor area.
Worked example
A living/dining L-shaped space measures 18 ft by 14 ft at its widest points, but a 6 ft by 5 ft corner is missing (perhaps where a hallway cuts in). Outer area = 18 × 14 = 252 sq ft. Cutout area = 6 × 5 = 30 sq ft. True area = 252 − 30 = 222 sq ft.
If your room has more than one notch
Break it into simpler shapes — treat each additional notch or jog as its own small area, and either add or subtract it from the main rectangle depending on whether it's an extension or a cutout.
Enter your outer dimensions and cutout size directly in the Square Footage / Area Calculator and it handles the subtraction for you.