Area Calculator
Calculate the area of common shapes — rectangle, square, circle, triangle, trapezoid, parallelogram, and ellipse. Enter your dimensions, and the result updates instantly with the formula shown. Works in any unit (cm, m, inches, feet) as long as you keep them consistent.
Area Formulas Used
- Rectangle — length × width
- Square — side × side
- Circle — π × radius²
- Triangle (base × height) — ½ × base × height
- Triangle (three sides) — Heron's formula: √(s(s−a)(s−b)(s−c)), where s = (a+b+c)/2
- Trapezoid — ½ × (side a + side b) × height
- Parallelogram — base × height
- Ellipse — π × semi-major axis × semi-minor axis
Frequently Asked Questions
What units should I use?
Any unit works as long as all dimensions are in the same unit. If you enter length in meters, enter width in meters too. The result will be in square units of whatever you entered (square meters, square feet, square inches). The optional unit field is just a label for the output.
How do I calculate the area of an irregular shape?
This calculator handles regular shapes only. For irregular shapes, break the area into simple shapes (rectangles, triangles), calculate each separately, and add the results. For land plots or floor plans with irregular boundaries, a dedicated land area calculator or CAD tool is more practical.
What is Heron's formula?
Heron's formula calculates the area of a triangle from its three side lengths, without needing the height. First compute the semi-perimeter s = (a + b + c) / 2, then the area = √(s(s−a)(s−b)(s−c)). It is useful when you can measure the sides but not the height.
What is the difference between area and perimeter?
Area is the space inside a shape, measured in square units. Perimeter is the distance around the shape, measured in linear units. A rectangle 5m × 3m has an area of 15 m² and a perimeter of 16 m. This calculator only returns area.
Can I calculate the area of a circle from its diameter?
Yes — divide the diameter by 2 to get the radius, then use π × radius². If you know the circumference instead, the radius is circumference ÷ (2π). The calculator asks for radius directly; convert diameter to radius first.
Is this calculator free and private?
Yes — completely free, no signup, no limits. All calculations run in your browser. No dimensions you enter are sent to a server or stored.