How to Calculate Square Footage: Rooms, L-Shapes and Circles
For most rooms, square footage is length times width. This guide covers that plus L-shapes, triangles and circles, with numbers you can check.
Rectangle or square room
Area = length x width, both in feet. A 12 ft by 15 ft room is 12 x 15 = 180 sq ft.
Measure in inches?
Convert to feet first by dividing by 12. A room 168 inches by 120 inches is 14 ft by 10 ft, which is 140 sq ft.
L-shaped or irregular rooms
Split the shape into rectangles, find each area and add them.
| Part | Size | Area |
|---|---|---|
| Main rectangle | 14 ft x 10 ft | 140 sq ft |
| Extension | 6 ft x 4 ft | 24 sq ft |
| Total | 164 sq ft |
Triangle
Area = 1/2 x base x height. Base 10 ft, height 6 ft: 0.5 x 10 x 6 = 30 sq ft.
Circle
Area = 3.1416 x radius x radius. A circle with a 5 ft radius: 3.1416 x 25 = 78.54 sq ft. If you know the diameter, halve it to get the radius.
Square feet to square yards
Divide by 9. A 180 sq ft room is 180 / 9 = 20 sq yd. Carpet is often sold by the square yard.
Measuring tips
- Measure at the widest points, wall to wall.
- Subtract large areas that will not be covered, such as a built-in cabinet.
- Add 5 to 10 percent extra for cuts and waste when buying flooring or tile.
- Round up. Running short costs more than a little extra.
Do it with a calculator
Skip the maths with the square feet calculator, then estimate materials with the flooring calculator or tile calculator. In Excel, use =A2*B2 with length in A2 and width in B2.
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Frequently asked questions
How do I calculate square footage of a house?
Add the square footage of each room measured wall to wall. Appraisers follow specific standards for what counts as living area, so check local rules for official figures.
How many square feet is 10 x 10?
100 square feet.
How do I calculate square feet from square meters?
Multiply square meters by 10.764.
How much extra flooring should I buy?
About 5 to 10 percent extra, more for diagonal patterns or rooms with many corners.
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