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Area Calculator: Rectangle, Circle, Triangle and More

This free area calculator works out the area, and where it applies the perimeter, of common flat shapes. Pick a shape, type the sizes and read the result in any unit you use.

By Debmedia Technologies LLP · Kolkata, India · Updated

What Is It and When Do You Need It?

Area is the amount of flat surface a shape covers. You need it to buy paint, tiles, carpet or turf, to plan a garden bed, or to answer a geometry question. Each shape has its own formula, and mixing them up is a common mistake.

Choose the shape and type the sizes that the label asks for. The tool also gives the perimeter where it can be found.

How to Use This Tool

  1. Pick the shape.
  2. Type the sizes a, b and c as described in the shape name.
  3. Press Calculate.
  4. Read the area and perimeter in your unit.

How the Calculation Works

Rectangle: a × b. Square: a². Triangle: ½ × base × height. Circle: π r². Trapezoid: ½ × (a + b) × height. Parallelogram: base × height. Ellipse: π × a × b. Sector: (angle ÷ 360) × π r². Perimeters: rectangle 2(a + b), square 4a, circle 2πr, ellipse by Ramanujan’s approximation, sector 2r + arc length.

Worked Example

A garden is 8 m long and 5 m wide, so the area is 40 m². A round table with radius 0.6 m covers π × 0.36 = 1.131 m². A triangle with base 10 and height 7 has area 35.

Common Uses

  • Buying flooring, paint or fertiliser.
  • Estimating land size.
  • School and exam geometry.
  • Planning layouts and gardens.

Tips and Common Mistakes

  • Use the same unit for every size.
  • Add 5 to 10 percent extra when buying materials for waste.
  • For odd shapes, split them into rectangles and triangles and add the areas.

Next, you may need the volume calculator, triangle calculator, Pythagorean theorem calculator, distance, midpoint and slope calculator.

Everything runs in your browser. Nothing you type is uploaded, stored or sent to any outside service.

Frequently Asked Questions

The same unit as your input, squared. If you type centimetres, the area is in square centimetres. The tool does not convert units.
π × r². With radius 5 the area is about 78.54 square units.
Use the labels in the shape list: a, b and c follow the order shown. Leave boxes empty if the shape does not need them.
A trapezoid perimeter needs the slanted sides, which are not given by the height alone, so only the area is shown.

Disclaimer: results are calculated in your browser from the numbers you enter. Check important results before you rely on them for money, health, safety or legal decisions.