# How to Find the Surface Area of a Sphere

## Learn how to calculate the surface area of a globe. Extension: Compare the size of the globe to the size of Earth.

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5 Steps
Supplies
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1

Measure the distance around the globe (unit: inches). Use the equator as the guide for your measuring tape (or string). Record the measurement from the tape or measure the length of the string.

2

This measurement of the distance around the globe gives you an estimate of the circumference of the globe. This circumference will be used to calculate the diameter of the globe.

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3

Find the diameter of the globe: divide the measured circumference by pi (3.14). Record the calculated diameter (unit: inches). Divide the diameter by 2 to find the radius (unit: inches).

4

Calculate the surface area of your globe with the following formula: Surface Area = 4 times 3.14 times radius squared. Record your estimate of the surface area of your globe (unit: inches squared).

5

Can measuring a globe help you understand the size of Earth? Use the Internet to research and find estimates for the circumference (unit: miles) and the surface area of Earth (unit: square miles).

### Supplies

 Measuring tape (or string and ruler) Globe Calculator Pencil Paper
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