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Area Calculator

Choose a shape, enter the measurements it needs and get its area. The calculator also shows the formula it used.

Shape

Rectangle: length. Square: side. Triangle: base. Circle: radius. Trapezium: first parallel side. Parallelogram: base.

Used by the rectangle (width) and the trapezium (second parallel side). Other shapes do not need it.

Used by the triangle, trapezium and parallelogram (perpendicular height). Other shapes do not need it.

This result is an estimate only. Check with your bank or the relevant authority before making decisions.

How it is calculated

  • Rectangle = a × b
  • Square = a²
  • Triangle = ½ × a × h (a is the base)
  • Circle = π × a² (a is the radius)
  • Trapezium = ½ × (a + b) × h
  • Parallelogram = a × h

If a shape needs b or h and it is empty, the calculator shows an error. Results are shown to four decimal places.

Worked example

  • Rectangle 10 × 5 = 50
  • Square with side 10 = 100
  • Triangle, base 10, height 4 = 20
  • Circle with radius 10 = 314.1593
  • Trapezium (10 + 5) × 4 ÷ 2 = 30
  • Parallelogram 10 × 4 = 40

Why your number may differ

All measurements must use the same unit. For a circle, enter the radius, not the diameter. For a triangle and a parallelogram, use the perpendicular height. If your textbook uses 22/7 for π, the circle answer can differ slightly.

Frequently asked questions

Which fields do I fill in for each shape?

Rectangle: a and b. Square: a. Triangle: a and h. Circle: a (the radius). Trapezium: a, b and h. Parallelogram: a and h.

What is the difference between height and slanted side?

The height is the perpendicular distance between the base and the opposite side, not the length of a slanted side.

What unit is the area in?

Area is in square units. If your measurements are in metres, the area is in square metres.

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