Square Footage Calculator
Calculate area in square feet for rooms, lawns and lots. Choose a shape, or add up to four rectangles for L-shaped and irregular spaces, then see the total in sq ft, sq yd, sq m and acres.
To find square footage, multiply length by width in feet: a 12 × 15 ft room is 180 square feet. For a circle use π × radius², for a triangle ½ × base × height. One square yard is 9 square feet and one acre is 43,560 square feet.
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How to calculate square footage
Square footage is the area of a flat surface measured in square feet. For any rectangular room or lot, multiply length by width (both in feet). A 12 ft × 15 ft room is 180 square feet. Other shapes have their own formulas:
| Shape | Formula |
|---|---|
| Rectangle / square | length × width |
| Triangle | ½ × base × height |
| Circle | π × (diameter ÷ 2)² — about 0.785 × diameter² |
| Trapezoid | ½ × (side A + side B) × height |
| Parallelogram | base × perpendicular height |
| Ellipse / oval | π × (width ÷ 2) × (height ÷ 2) |
| Circle sector | π × radius² × angle ÷ 360 |
How to measure an L-shaped or irregular space
Split the space into rectangles, measure each, and add the areas. Choose Several rectangles above and enter up to four sections. For a whole house, list each room separately and add them. Subtract anything that isn't part of the surface — a kitchen island, a fireplace hearth, or a patio inside a lawn.
Worked example: an L-shaped living and dining area
Split the space into two rectangles: the living room is 18 × 12 ft = 216 sq ft and the dining nook is 10 × 8 ft = 80 sq ft, so the total is 296 sq ft (32.9 sq yd). Flooring with 7% waste means buying about 317 sq ft; at $3.50 per square foot that is roughly $1,109 in material.
Common room sizes in square feet
| Room size | Square feet | Square yards |
|---|---|---|
| 10 × 10 ft | 100 | 11.1 |
| 10 × 12 ft | 120 | 13.3 |
| 12 × 12 ft | 144 | 16.0 |
| 12 × 15 ft | 180 | 20.0 |
| 12 × 20 ft | 240 | 26.7 |
| 14 × 16 ft | 224 | 24.9 |
| 15 × 20 ft | 300 | 33.3 |
| 20 × 20 ft | 400 | 44.4 |
| 20 × 30 ft | 600 | 66.7 |
Unit conversions
| From | To |
|---|---|
| 1 square yard | 9 square feet |
| 1 square meter | 10.764 square feet |
| 1 acre | 43,560 square feet |
| 1 square foot | 144 square inches |
What square footage is used for
Flooring, tile, paint, sod, roofing, insulation and carpet are all bought by area. Once you have the square footage, add a waste allowance (typically 5–10%) and use the right calculator: flooring, paint, tile, carpet or sod. Real-estate listings often quote gross living area, which counts finished, heated space only and excludes garages, porches and unfinished basements.
Frequently asked questions
How do I calculate square feet of a room?
Measure the room's length and width in feet and multiply. A 12 ft × 15 ft room is 180 square feet.
How do I calculate square footage of an L-shaped room?
Divide it into two rectangles, find the area of each, and add them together. The calculator above lets you enter up to four sections.
How many square feet are in a square yard?
9 square feet. Carpet is sold by the square yard, so divide square feet by 9.
How do I convert square inches to square feet?
Divide by 144, since a square foot contains 12 × 12 = 144 square inches.
How many square feet are in an acre?
One acre is 43,560 square feet — roughly a football field without the end zones.
How do I find the square footage of a circle?
Square the radius (half the diameter) and multiply by 3.1416. A circle 10 feet across has about 78.5 square feet.
How do I calculate square footage in meters?
Choose Meters in the unit menu. One square meter is 10.764 square feet.
Does square footage include walls?
For a room, measure wall to wall (inside dimensions) for flooring and paint calculations. Listings may use outside measurements, so they can be slightly larger.
Sources and further reading
- NIST Special Publication 811: conversion factors — National Institute of Standards and Technology
These references support the general guidance on this page. The calculator applies the standard formulas shown above to the numbers you enter.
Related calculators
. Estimates only. Always confirm quantities with your supplier or a qualified contractor before ordering, and add extra for waste and site conditions.