Square Footage Calculator

A square footage calculator returns the area in square feet for a rectangle, a circle, or a triangle. Rectangles use length × width. Circles use π × radius², with the radius taken as half the diameter. Triangles use (base × height) ÷ 2, with the height measured perpendicular to the base.

Last reviewed September 2026Method & sources Report an error

Not to scale.

Area

120 sq ft

Breakdown
Area	120 sq ft

How to Calculate Square Footage

A rectangle's area is simply length × width. A circle's area is `π × radius²`, using half the diameter as the radius. A triangle's area is `(base × height) ÷ 2`, where height is measured perpendicular to the chosen base, not along one of the triangle's slanted sides.

Example: 12 ft × 10 ft rectangular room

A 12 ft × 10 ft rectangular room: Area: 12 × 10 = 120 sq ft A 10 ft diameter circle instead: π × (10 ÷ 2)² = π × 25 = 78.54 sq ft. A triangle with a 12 ft base and 10 ft height instead: (12 × 10) ÷ 2 = 60 sq ft.

Square Footage: Compare Scenarios

Scenario	Area
Small (8×8 ft bathroom)	64 sq ft
Medium (12×10 ft bedroom)	120 sq ft
Large (20×15 ft living room)	300 sq ft

What Is Square Footage?

A square footage calculator converts a shape's dimensions into its area in square feet. It is the starting measurement behind most other material calculators on this site, for flooring, paint, gravel, or any other coverage-based project. This calculator handles the three most common shapes directly: rectangle, circle, and triangle.

Square Footage: Pros and Cons

Pros

Handles the three most common shapes people need to measure (rectangle, circle, and triangle) in one calculator
Uses the exact formula for each shape rather than an approximation
A natural first step before using any of this site's material calculators, most of which start from an area figure

Cons

Doesn't handle an irregular or L-shaped area directly. Break it into rectangular, circular, or triangular sections, calculate each separately, and add the results together
A triangle's height must be measured perpendicular to the base, not along a slanted side. Using the wrong measurement gives an incorrect area
Doesn't convert to other area units (like square yards or acres). See the Acreage calculator for a sq ft to acres conversion

Square Footage: What a Pro Checks

Break an irregular or L-shaped room into rectangular, circular, or triangular sections, find each section's area separately, then add them together. Forcing one formula onto a non-standard shape gives a wrong number.
Measure a triangle's height perpendicular to the base, not along one of its slanted sides. Using the slanted measurement instead of the true perpendicular height is a common source of an incorrect area.
For a circle, measure the diameter (straight across through the center) rather than trying to measure the radius directly. It's the easier, more accurate field measurement, and this calculator halves it for you.

Frequently Asked Questions

How do I calculate square footage of a room?

For a simple rectangular room, multiply length by width. A 12 ft × 10 ft room is 120 sq ft.

How do I calculate the square footage of a circle?

Use π × radius², where radius is half the diameter. A 10 ft diameter circle has a radius of 5 ft, giving an area of π × 25 ≈ 78.54 sq ft.

How do I find the square footage of a triangular area?

Multiply the base by the height (measured perpendicular to that base, not along a slanted side) and divide by 2. A triangle with a 12 ft base and 10 ft height has an area of (12 × 10) ÷ 2 = 60 sq ft.

How do I calculate square footage of an irregular room?

Break the room into simpler rectangular, circular, or triangular sections, calculate each section's area separately, then add them together for the total.

What is the difference between square footage and square yards?

Square yards are square feet divided by 9 (since 1 sq yd = 3 ft × 3 ft = 9 sq ft), a unit commonly used for carpet and some flooring pricing. This calculator gives square feet. Divide by 9 to convert to square yards.

Measurement