Calculating a square area is as easy as multiplying the length by the width. But when you have a curved surface like a sphere or a cylinder, the problem can be puzzling. Luckily, mathematicians have figured out formulas for curved surfaces, so all you have to do is take a couple of simple measurements and plug the measurements into the formulas. For example, if you know the radius of a sphere, you can use the formula 4 pi r^2 to calculate its surface area. The surface area of a cylinder can be calculated with the height and radius using the formula 2 pi r^2 + 2 pi r h.

### Surface Area of a Sphere

Square the radius. For example, if the radius is 5 inches, then: 5 inches * 5 inches = 25 inches squared.

Multiply Step 1 by pi. Pi * 25 inches squared = 78.54 inches squared.

Multiply Step 2 by 4: 78.54 inches squared * 4 = 314.16 inches squared.

### Cylinder

Square the radius. For example, if the radius is 2 inches, then: 2 inches * 2 inches = 4 inches squared.

Multiply Step 1 by 6.28. 6.28 * 4 inches = 25.04 inches.

Multiply the radius by the height. For example, a radius of 2 inches and a height of 10 inches would give you: 2 inches * 10 inches = 20 inches squared.

Multiply Step 3 by 6.28: 20 inches squared * 6.28 = 125.6 inches squared.

Add Step 2 and Step 4 together: 25.04 inches squared + 125.6 inches squared = 150.64 inches.

#### Tip

Although 3.14 is a good approximation of pi and will work for most calculations, you can increase the accuracy of your answers by adding more decimal places to pi. For example, use 3.1416 for pi (4 decimal places) and 6.2832 for 2pi.