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Square Footage Calculator

Use this square footage calculator to find the area of a rectangle, a circle or a triangle in square feet, square yards and acres, then go to the page for your job.

  • Instant answer as you type
  • Nothing you type is sent anywhere
  • Worked example with clear steps

Your measurements

ft
ft
Price per square foot (optional)

The price is yours: we state none, and we store and show no prices. The limit of 1,000,000 is ours.

$ per ft²

Result

Calculated live
Square feet
300 ft²
Square yards 9 ft² in a yard
33.33 yd²
Acres 1 acre is 43,560 ft²
0.0069 acres
Square meters 1 ft² is 0.09290304 m²
27.87 m²

Based on NIST SP 811 NIST Handbook 44, Appendix C Home Innovation, ANSI Z765 Full list of sources

Assumptions and constants

You can change

Fixed values (exact definitions and references)

These are exact definitions and cannot be edited.

Square feet in a square yard Reference [1]

9 ft² per yd²

3 ft × 3 ft. NIST gives the yard as exactly 0.9144 m and the foot as exactly 0.3048 m.

Square feet in one acre Reference [2], [1]

43,560 ft² per acre

NIST Handbook 44 gives 43,560 square feet in an acre.

How to use the square footage calculator

  1. Pick Rectangle, Circle or Triangle, then enter its size in feet.
  2. Read Square feet and Square yards.
  3. For a price, open Price per square foot (optional) and enter your Price per square foot.
  4. Use Copy result or Print, and check the area against your plan.

How do I calculate square footage?

For a rectangle, multiply the length in feet by the width in feet. A square yard is 9 square feet, and an acre is 43,560 square feet. [2] A square foot is 0.09290304 square meters. [1]

Worked example

A rectangle 20 ft long and 15 ft wide is 20 x 15 = 300 square feet. Divided by 9, that is 33.33 square yards. Divided by 43,560, it is 0.0069 acres.

Rectangle: length 20 ft, width 15 ft A rectangle seen from above, a little longer than it is wide. Its length, 20 ft, is marked under it and its width, 15 ft, along the right side. From above Length 20 ft Width 15 ft
Drawn to scale for a rectangle 20 ft long and 15 ft wide. The calculator turns the size into square feet, square yards and acres.

Square footage of a circle or a triangle

A circle is pi x the radius x the radius: a circle 20 ft across has a radius of 10 ft, so 3.1416 x 10 x 10 = 314.16 square feet. A triangle is its base x its height / 2: a base of 20 ft and a height of 15 ft is 20 x 15 / 2 = 150 square feet. Pick the shape above.

How do I calculate the square footage of a house?

Find the area of each floor and add them. A floor 30 ft by 20 ft is 600 square feet, so two floors of that size are 1,200. For each room on a floor, the room square footage calculator takes feet and inches.

What counts as square footage?

Home Innovation Research Labs says the ANSI Z765 standard covers the calculation and reporting of above-grade and below-grade square footage in single-family houses. [3]

We found no source we can read for which floors, walls, stairs or ceiling heights count, so this page does not decide that. Ask the person who measured the house which method they used.

Does square footage include the garage?

We found no source we can read that says whether a garage is counted. Ask who measured the house, and ask for the area of the garage on its own.

Square footage when selling a house

We found no source for how a seller, a builder and an appraiser each count. The appraiser's method is the one named in the answer on who measures a house.

How do I find the square footage of a roof?

A roof is measured along its slope, not across its footprint. The roofing calculator finds the roof area from the footprint and the pitch, and the roof pitch calculator gives the slope.

How do I work out a price per square foot?

The cost is the area times the price per square foot. Open the section Price per square foot (optional) above and enter your price. We state no price, and the site does not store the prices you type.

How to split rent by square footage

A unit's share is its area divided by the total area. A unit of 600 square feet in a building of 1,800 square feet has a share of 600 / 1,800 = 0.3333, which is one third. Multiply the share by the total rent to find the unit's part.

Which area calculator for your job?

Common mistakes and limits

  • Mixing units. Enter every size in feet. For inches, use the room page.
  • Using the diameter as the radius. The circle option asks for the diameter, the width across.
  • What this tool does not cover: how a house is measured for sale, and the rules of your area.

Frequently asked questions

Is square footage length times width?

For a rectangle, yes: the length in feet times the width in feet. A circle is pi times the radius squared, and a triangle is its base times its height divided by 2. Pick the shape above.

Where can I find the square footage of a property?

We found no source we can cite for where it is recorded. Ask the seller, your local assessor or the listing, and measure it yourself to be sure.

Who measures the square footage of a house?

Home Innovation Research Labs says Fannie Mae requires appraisers to use the ANSI Z765-2021 method to determine gross living area. A seller or a builder may use another method. [3]

Is there a calculator for one room?

Yes: the room square footage calculator takes feet and inches, and an L-shaped room as two rectangles.

Sources and references

  1. National Institute of Standards and Technology (NIST). NIST Guide to the SI, Appendix B.8: Factors for Units Listed Alphabetically (SP 811, accessed November 2026). Used for: the inch and foot relationship and the square meters in a square foot.
  2. National Institute of Standards and Technology (NIST). Handbook 44, Appendix C, General Tables of Units of Measurement (2026, accessed November 2026). Used for: the 9 square feet in a square yard and the 43,560 square feet in an acre.
  3. Home Innovation Research Labs. Square Footage Method for Calculating, ANSI Z765, frequently asked questions (accessed November 2026). Used for: what the ANSI Z765 square footage standard covers, and who must use it.

How we use sources: methodology.

Estimates only. Confirm quantities with your supplier. See the disclaimer. Found a wrong result? Report an error.