A cylinder is a three-dimensional object that looks like a rod with circular ends. The radius of a cylinder is the distance from the center of one of the circular faces to its edge. If you know the volume and the height of a cylinder, you can find its radius by using the formula for the volume of a cylinder.

**Know the Formula for the Volume of a Cylinder**

The formula for the volume of a cylinder contains three elements: the radius of the cylinder (r), the height (h) of the cylinder, and the ratio of the circumference of a circle to its diameter *pi*. To find the volume of a cylinder, you multiply *pi* by the cylinder's height and the square of its radius. Here is the formula in mathematical terms:

V = pi x h x r^2

**Solve for the Radius (r)**

Since you want to find the radius of the cylinder, you need to rearrange the formula to solve for the term r, which is the radius. First, divide both sides by *pi* and h. These terms will cancel on the right side of the equation, leaving only r^2. Now take the square root of both sides to get rid of the square on the radius. This leaves us with the following:

r = square root of (V / (pi x h))

**Plug in the Values for Height (h) and Volume (V) and Calculate**

Now just plug your numbers into the equation and compute the radius. For example, if your cylinder has a height of 10 centimeters and a volume of 30 cubic centimeters, the calculation would look like the following:

r = square root of (30 cm^3 / (3.14 x 10 cm)) = 0.98 cm

#### Tip

Remember: pi is always equal to approximately 3.14.

Always remember to include your units in your calculations and especially in your answer.