Area Calculator

Area of any common shape

Area is the amount of surface a flat shape covers, measured in square units. Pick a shape and enter its dimensions, and this calculator returns the area along with the formula it used. It's unit-agnostic: enter centimeters and you get cm², enter feet and you get ft² — the math is the same.

The formulas

• Rectangle: length × width
• Square: side²
• Triangle: ½ × base × height
• Circle: π × radius²
• Trapezoid: ½ × (a + b) × height — the average of the two parallel sides, times the distance between them
• Parallelogram: base × height (the perpendicular height, not the slanted side)
• Ellipse: π × a × b, where a and b are the two semi-axes

The most common mistake: height vs. side

For triangles and parallelograms, "height" means the perpendicular distance — a straight line from the base to the opposite point or side, at a right angle. It is not the length of a slanted edge. Using a slanted side instead of the true height is the usual reason an area comes out too big.

Putting area to use

Area answers practical questions: how much paint, flooring, turf, or fabric you need; the size of a room or plot; how much material a project takes. For odd shapes, split the shape into rectangles and triangles, find each area, and add them together.

FAQ

What units does it use?

Whatever you enter. The result is always in those units squared. Just keep every input in the same unit — don't mix feet and inches in one calculation.

How do I find the area of a circle from its diameter?

Halve the diameter to get the radius, then enter that. The radius is always half the diameter.

How do I calculate the area of an irregular shape?

Break the shape into simple rectangles, triangles, and circle segments, calculate each piece with this tool, then add the results. For a curved or truly irregular outline, approximate it with several rectangles or triangles and sum them.

Is this area calculator free to use?

Yes, it is completely free with no sign-up or limits. You can calculate as many shapes as you like.

Does it run in my browser, and does it work on mobile?

All calculations run locally in your browser, so nothing you type is uploaded anywhere. It works on phones, tablets, and desktops in any modern browser.

How do I convert between square units like square feet and square meters?

This tool returns the result in the same unit you enter, squared, so it does not convert between unit systems. To convert afterward, remember that one square meter is about 10.76 square feet, and one square foot is about 144 square inches.