# How to find the radius of a cone

Written by frank luger
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A cone is a tapering three-dimensional geometric shape with a flat, circular face at one end and a point called the apex at the other end. An object which has a shape like a cone is often referred to as conical. Examples of some commonly found conical shapes are an ice-cream cone, a conical party hat and a traffic cone. Ellipses, which are geometrically related to cones, can be obtained by cutting up cones, according to mathematician J. W. Downs.

Skill level:
Easy

### Things you need

• Ruler
• Pencil
• Paper
• Calculator (if necessary)

## Instructions

1. 1

Let x be equal to the radius of the cone, as x is the thing you are attempting to discover. Write down “2 x =”.

2. 2

Lay your ruler across the widest part of the circular face of the cone, which is known as the diameter. Write down the measurement after “2 x =”, for example: “2 x = 10 cm”.

3. 3

Find x by dividing the diameter measurement by 2. For example, if the diameter is 10 cm, x = 5 cm. Use a calculator for this calculation if necessary. Note that the radius is half of the diameter, as it is a measurement from the edge of the circle to the centre point.

4. 4

Write down “The radius of the cone is” and then write down the figure you arrived at in step 3.

#### Tips and warnings

• If you know only two variables of the cone, use a Cone Calculator to calculate other properties.
• The point of a cone is sharp and appropriate care should be taken when handling it.

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