How to use the area calculator
Choose the shape, then enter the requested dimensions using the same unit. The result is expressed in square units because area measures a two-dimensional surface.
Area formulas
If the dimensions are in feet, the result is square feet. If they are in inches, the result is square inches.
Example: Zoe measures a circular space
Zoe measures a circle with a radius of 5 meters. Area is π × 5² = 25π, approximately 78.54 square meters.
If the measurement is the diameter, divide it by two before entering the radius. Doubling the radius multiplies the area by four, because the radius is squared.
Area formulas depend on the shape
A rectangle uses length x width. A triangle uses one-half x base x perpendicular height. A circle uses pi x radius squared.
Choose the shape that matches the dimensions you actually have. A triangle's slanted side is not a substitute for perpendicular height unless the geometry makes them the same.
Area is measured in square units
If the input dimensions are in feet, the area is in square feet. If they are in meters, the area is in square meters. Multiplying two lengths creates a two-dimensional unit.
For a composite shape, calculate non-overlapping component areas and add or subtract them as needed.
Assumptions and limitations
What the estimate assumes
Complex or irregular shapes should be divided into simpler shapes or measured with a specialized tool.
Area Calculator FAQs
Why is area measured in square units?
Area describes two-dimensional space, so both dimensions contribute a unit factor.
What is the area of a rectangle?
Length multiplied by width.
What is the area of a triangle?
One-half times base times perpendicular height.
What is the area of a circle?
Pi times the radius squared.
What is the formula for rectangle area?
Rectangle area equals length multiplied by width.
What is the formula for circle area?
Circle area equals pi multiplied by the square of the radius: A = pi r^2.
General geometry calculator. Use consistent units for all dimensions.