ClaruSite
🏠 Home & Garden

Square Footage Calculator · Rooms, Walls and Irregular Lots

Square footage is the number behind almost every home project: how much flooring to buy, how much paint a wall needs, what a room rents for or what a lot is worth. It is also easy to get wrong when the space is not a plain rectangle. This calculator finds the area of a rectangle, an L-shaped room, a triangle, a trapezoid, a circle, a semicircle and an irregular four-sided lot, and gives the answer in square feet, square yards, square meters, acres and square inches.
Pick the shape, choose the unit you measured in (feet, inches, yards or meters) and enter the dimensions. Use decimals for partial feet: 10 feet 6 inches is 10.5. To leave out doors, windows or columns, enter their area in square feet in the subtract field. To buy material, set the extra for waste and the calculator adds it to the area, and if you enter a price per square foot it returns the total cost.
For an irregular lot, measure the four sides in order and, if you can, the diagonal between two opposite corners. With the diagonal the lot is split into two triangles and the area is exact. Without it the calculator uses the surveyor's rule of thumb, which is exact for a rectangle but only an estimate for other shapes, and it tells you so. For a legal boundary or a property sale, rely on a licensed surveyor.
Use decimals: 10 ft 6 in is 10.5 feet
Standard: 10
Doors, windows, columns or any area you do not want counted
Standard: 10
Material, labor or property value, to get a total cost
Room size:
Subtract:
Unit:
Extra:

Detailed Breakdown

6 metrics
PRIMARY RESULT
120.00 square feet
Total Area
Square Yards
13.33 square yards
Square Meters
11.15 square meters
Acres
0.00275 acres
Square Inches
17,280 square inches
Area to Buy With 10% Extra
132.00 square feet

Related Calculators

4 tools
Mulch, Gravel & Topsoil Calculator · Cubic Yards, Bags and Tons
Home & Garden
Open
Roofing Calculator · Roof Area, Squares and Shingle Bundles
Home & Garden
Open
Paint Calculator · How Many Gallons Do You Need?
Home & Garden
Open
Tile & Flooring Calculator · How Many Tiles and Boxes Do You Need?
Home & Garden
Open

Behind this is dedication and a desire to help

ClaruSite is 100% free and independent. Your support helps keep these financial tools fast, accurate, and available to everyone.

PayPalDonate with PayPal
exploreReal-World Scenarios

When to Use This Calculator

Everyday financial situations where this tool gives you fast, accurate clarity:

🏠

Buy Flooring or Tile

Get the area of a room and add the extra you need for cuts and waste.

🎨

Measure Walls for Paint

Subtract doors and windows to find the wall area that actually gets painted.

📐

Measure an Irregular Lot

Use four sides and a diagonal to get the area of a lot that is not a rectangle.

🔄

Convert Between Units

See square feet, square yards, square meters, acres and square inches at once.

Calculation Formula

Standard Method

Rectangle: Area = Length × Width L-shape or two rectangles: Area = (A length × A width) + (B length × B width) Triangle: Area = Base × Height ÷ 2 Trapezoid: Area = (Longer side + Shorter side) ÷ 2 × Height Circle: Area = π × Radius²; semicircle: half of that Four-sided lot with a diagonal: split along the diagonal into two triangles. For sides a, b and the diagonal, s = (a + b + diagonal) ÷ 2 and Area = √(s × (s − a) × (s − b) × (s − diagonal)) (Heron's formula). Add the second triangle, sides c, d and the diagonal. Four-sided lot without a diagonal (estimate): Area = (a + c) ÷ 2 × (b + d) ÷ 2 Units: 1 yard = 3 feet, 1 inch = 1/12 foot, 1 meter = 3.2808 feet. Square yards = square feet ÷ 9. Acres = square feet ÷ 43,560. Square meters = square feet × 0.092903. Area to buy = Area × (1 + Extra %).

Benchmark Example:
A 12 ft by 10 ft room: • Area: 12 × 10 = 120 square feet • In other units: 13.33 square yards, 11.15 square meters, 17,280 square inches • With 10% extra for flooring: 132 square feet to buy • At $4 per square foot: 120 × $4 = $480, or $528 with the extra An L-shaped room made of a 10 × 8 ft section and a 6 × 4 ft section: 80 + 24 = 104 square feet. An irregular lot with sides of 100, 100, 60 and 80 feet and a 120-foot diagonal: • Triangle 1 (100, 100, 120): s = 160, area = √(160 × 60 × 60 × 40) = 4,800 sq ft • Triangle 2 (60, 80, 120): s = 130, area = √(130 × 70 × 50 × 10) = 2,133.07 sq ft • Total: 6,933.07 square feet, or 0.159 acres • Without the diagonal the rule of thumb gives (100 + 60) ÷ 2 × (100 + 80) ÷ 2 = 7,200 sq ft, about 4% too high, which is why the diagonal is worth measuring.

Frequently Asked Questions

8 answers

Applicable Laws & Regulatory Standards

American National Standards Institute & National Institute of Standards and Technology

Official Legal Reference
ANSI Z765-2021 — Square Footage: Method for Calculating

The American National Standard for measuring single-family homes, which measures finished above-grade space from the exterior walls. It explains why a listing can differ from the sum of the interior rooms you measure with this calculator.

NIST Special Publication 811 — Guide for the Use of the International System of Units (SI), Appendix B

Gives the exact conversion between US customary and metric units (1 foot = 0.3048 meter), which this calculator uses to convert square feet, square yards and square meters.

NIST Handbook 44, Appendix C — General Tables of Units of Measurement

Lists the units of area used in the United States, including the acre of 43,560 square feet and the square yard of 9 square feet.

Legal citations and statutes are provided for consumer transparency, analytical validation, and educational reference under U.S. consumer financial regulations. This tool is not a substitute for formal legal, accounting, or tax counsel.

💡

Found an error or have a suggestion?

Help us calibrate this tool for US regulations and consumer standards.

Send Feedback
Related Calculators for Better Decisions
Mulch, Gravel & Topsoil Calculator · Cubic Yards, Bags and TonsRoofing Calculator · Roof Area, Squares and Shingle BundlesPaint Calculator · How Many Gallons Do You Need?Tile & Flooring Calculator · How Many Tiles and Boxes Do You Need?