The circumference of a circle will be discovered utilizing both C = π × d or C = 2 × π × r. The lesson about the quantity π reveals tips on how to derive the system.

If both the radius of a circle (r) or the diameter of the circle (d) is understood, you will discover the circumference by merely substituting the recognized worth for r or d within the system. Use 3.14 for π.

## A couple of examples exhibiting tips on how to discover the circumference of a circle

**Examples #1**

Calculate the circumference of a circle if r = 2 inches

C = 2 × π × r = 2 × 3.14 × 2 = 12.56 inches

**Examples #2**

Calculate the circumference of a circle if r = 4 inches

C = 2 × π × r = 2 × 3.14 × 4 = 25.12 inches

**Examples #3**

If D = 10 cm, discover the circumference.

You’ve two selections. You possibly can first discover r after which substitute its worth for r within the system.

r is half the diameter, so r = 10 divided by 2

r = 5 cm

C = 2 × π × r = 2 × 3.14 × 5 = 31.4 cm

In any other case, you may simply use the system C = π × D

C = 3.14 × 10 = 31.4 cm

## A difficult train in regards to the circumference of a circle

**Examples #4**

The circumference of circle A is 4 instances the circumference of circle B

The diameter of circle B is 7. What’s the diameter of circle A?

Let C_{A} be the circumference of circle A

Let C_{B} be the circumference of circle B

Let D_{A} be the diameter of circle A

Let D_{B} be the diameter of circle B

Because the ratio of circumference to diameter is identical for all circles, you should use the next proportion to resolve this downside.

**Issues that we all know**:

C_{A} = 4 × C_{B}

D_{B} = 7

Substitute these within the proportion

=
8 then, 2 × 20 = 5 × 8 |

=
C then, 4 × C |

28 × C_{B} = D_{A} × C_{B}

D_{A} = 28 since 28 × C_{B} = 28 × C_{B} it doesn’t matter what C_{B} is

**Issues that we all know**:

C_{A} = 4 × C_{B}

D_{B} = 7

Substitute these within the proportion

=
8 then, 2 × 20 = 5 × 8 |

Then, 4 × C_{B} × 7 = D_{A} × C_{B}

28 × C_{B} = D_{A} × C_{B}

D_{A} = 28 since 28 × C_{B} = 28 × C_{B} it doesn’t matter what C_{B} is

## Circumference of a circle quiz. See how effectively you may calculate the circumference or perimeter of a circle