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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How to Find the Surface Area of a Sphere
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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.

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.

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).

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).

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).

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).

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