# Area of a circle

The area of a circle is the amount of space within its boundary line or circumference.

Circle area from circle radius

where

Given a circle with radius 7cm (centimeters), its area A = π x 7*² = 153.9*c*m² (square centimeters) to 1 d.p. (one decimal place).*

*To square the radius r on your calculator you'll need to use **x**²**. Press the pi sign (**π) followed by the multiply sign (x), enter 7, then press **x**² followed by the equals sign (=). 153.93804 should be displayed which is 153.9 to 1 d.p. **You may need to access** x**² and* *π* via a shift or 2nd function button.

When the circle's radius is 13m (meters), the area of the circle A = π x 13*²** = 530.93**m² (square meters) to 2 d.p. (two decimal places).*

*On your calculator, enter pi sign (**π), multiply sign (x), 13, **x**², equals sign (=) to give 530.9291585 = 530.93 to 2 d.p.*

## Circle area from circle diameter

Let's say the circle's diameter d = 4.5 cm. Area A = π (4.5 / 2)*²* = 15.9cm*²* to 1 d.p.

*Use your calculator's left and right bracket signs*

*The key strokes are left bracket sign, 4.5, divide sign (*÷*), 2, right bracket sign,** x**²*, multiply sign (x), pi sign (*π), **equals sign (=), giving 15.90431281 which is 15.9 to 1 d.p.*

What about the area of a circle with diameter d = 16m?

**Area of circle A = π (16 / 2)***² * = 201.06m*²* to 2 d.p.

*On your calculator, enter in order left bracket sign, 16, divide sign (*÷*), 2, right bracket sign,** x**²*, multiply sign (x), pi sign (*π), **equals sign (=). The display should show 201.0619298 = 201.06 to 2 d.p.*

## Circle area from circle circumference

- A = area of circle
- π = pi
- C = circumference of circle

If the circumference of a circle C is 29cm, then its area A = π [29 / (2π)]*² = 66.9cm**²* to 1 d.p.

*Enter 29 on your calculator, then divide sign (**÷)**, left bracket sign, 2, multiply sign (x), pi sign (π), right bracket sign, equals sign (=),** x**²,* multiply sign, pi sign (*π), equals sign (=). 66.92465357 should be displayed which is 66.9 to 1 d.p.*

Next consider a circle with circumference C = 1.5m.

**Area of circle A = π [1.5 / (2π)]***² = 0.18m**²* to 2 d.p.

*Enter 1.5 instead of 29, otherwise use
the same key strokes on your calculator to give 0.179049311 = 0.18 to 2 d.p.*

## Now use some of your own figures to practice calculating the area of a circle

Do the same for the radius, diameter and circumference of a circle and you'll soon get to grips with circle calculations!

For more on the circle click:

Radius of a circle

Diameter of a circle

Circumference of a circle

Pi (π)

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Area of a circle