HowMuchIt / Square feet
How do I calculate square footage?
Length times width, in feet: that is a room's square footage. The calculator adds the odd shapes, and the page explains what a home's official square footage leaves out.
Work out your square footage
| Shape or unit | How |
|---|---|
| Rectangle | length x width |
| Triangle | base x height / 2 |
| Circle | 3.14 x radius x radius (radius = half the width across) |
| Inches | inches / 12, added to the feet: 12 ft 6 in = 12.5 ft |
| Square yards | sq ft / 9 |
| Square meters | sq ft x 0.0929 (1 sq m = 10.764 sq ft) |
Measuring a room the easy way
Measure along the floor, wall to wall, to the nearest inch, and write each number down. Inches become feet when you divide by 12, so 12 feet 6 inches is 12.5 feet. A room shaped like an L is two rectangles: measure each one and add them. A bay window or a half-round patio is a rectangle plus a half circle; a sloped corner of a garden is a triangle. Closets and hallways count, so measure them too if the floor or the paint goes there.
What a home's square footage counts
When a house is sold or appraised, its square footage follows a standard, ANSI Z765, and it is not the same thing as adding up the rooms. It counts only finished, heated space above ground, measured from the outside of the exterior walls, with ceilings at least 7 feet high. Under a sloped ceiling, at least half the floor needs 7 feet of headroom, and any part under 5 feet is left out. Garages and unfinished attics do not count, and a basement, even a finished one, is reported on its own line. Stairs count with the floor they go down from.
Questions people ask
How many square feet is a 12 x 12 room?
144 square feet: 12 times 12. That is 16 square yards, or about 13.4 square meters.
How do I measure a room with odd wall sizes?
Split the floor into rectangles and triangles you can measure, work out each one, and add them. The calculator takes four shapes at once.
Is a garage included in square footage?
Not in a home's official square footage, and an unfinished attic is not either. For your own project, like a new garage floor, measure it the same way as any room.
Do finished basements count?
They are below grade, so the standard reports them apart from the main square footage, even when finished.
Can I measure my house myself?
Yes: measure the outside walls to the nearest inch, then round the total to the nearest whole square foot, as the standard does. An appraiser's number can still differ if parts do not meet the rules above.
How big is my garden bed or lawn?
The same way: a rectangular bed is length times width, a round one is 3.14 times the radius times itself. Then the mulch calculator turns square feet and a depth into bags.
Good to know
- The area of a square or rectangular room is its length times its width, both measured in feet; the answer is in square feet.1,2,3,4
- For an L-shaped or irregular room, split the floor into rectangles, work out each area separately, then add the areas together.1,2,3,5
- The area of a triangle is its base times its height, divided by 2.4,5,6
- The area of a circle is pi (about 3.14) times the radius squared; the radius is the distance from the center to the edge.3,4,6
- To turn inches into feet, divide the inches by 12 and add the result to the whole feet (for example 12 ft 6 in = 12.5 ft).7,8
- One square yard equals 9 square feet, so divide square feet by 9 to get square yards.7,9
- One square foot equals 0.0929 square meters, and one square meter equals about 10.764 square feet.10,11,12
- Measure each length to the nearest inch (or tenth of a foot); the ANSI home standard then reports the total to the nearest whole square foot.7,13,14
- Under the ANSI Z765 standard used by appraisers, a home's square footage counts only finished, heated, above-grade space with a ceiling at least 7 feet high.2,13,14,15
- In a room with a sloped ceiling, at least half of the floor must have 7 feet of headroom, and any part under 5 feet is left out.13,14
- Basements, even finished ones, are below grade and are reported separately rather than added to the home's main square footage.2,13
- Garages and unfinished attics are not counted in a home's square footage.2,3,13
- For a house, the official square footage is measured from the outside of the exterior walls, so it includes the wall thickness.2,13,14
- Stairs count in the square footage of the floor they go down from.2,13,14
- Closets and hallways are included in a home's square footage, so measure them too.2,3,8,15
How we checked this page
Checked on October 27, 2026. We kept a fact only when two independent publishers agree, and each one is numbered to its sources below. Where sources give different numbers, we keep only what they share. We never write a price. This page was written with an AI assistant and checked against the sources below.
Sources
- 4 Steps to Calculate Square Footage, The Home Depot
- How to Accurately Calculate Square Footage of a House, Redfin
- How to Calculate the Square Footage of a House, Chase
- Garden Math (Home Gardeners, Sarah Browning), Nebraska Extension in Lancaster County
- Measuring the Area of a Home Lawn (HGIC 1220), Clemson Cooperative Extension, Home & Garden Information Center
- Garden Math: Calculating the Area and Depth of Your Garden, Fine Gardening
- Square Footage Calculator: How to Measure Any Room's Sq Ft, Carpet One Floor & Home
- How to Calculate Square Footage for Flooring, CALI (Cali Floors)
- Carpet Calculator, HomeAdvisor
- NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity, NIST (US government)
- Square foot, Wikipedia
- Square metre, Wikipedia
- Understanding Gross Living Area: The ANSI-Z765-2021 Standard, McKissock Learning
- Understanding ANSI Measurement Standards (WREM August 2022), Wisconsin REALTORS Association
- How to Take Your Home's Measurements and Estimate Value, HomeLight