Circle Perimeter Calculator

If you don’t know how to find the circumference of a circle, our calculator is the fastest option. Even so, it's helpful to understand how equations work to interpret the results better. The circle perimeter formula is:

p = 2πr

where p is the circle's perimeter, r is the radius, and π is a constant equal to approximately 3.14159265...

You can also express the perimeter in terms of the diameter (d), remembering that r = d/2:

p = πd

Finally, let’s remember the circle area (A) can be expressed as A = πr², allowing us to obtain a new formula for the circle perimeter based on its area:

p = 2√(πA)

💡 The number π is a constant equal to the ratio of the circumference to the diameter (or twice the radius). It'll always have the same value, independently of the size of the circle. Solving for π in the above equation results in the mentioned ratio: π = p/(2r).

Half-circle and quarter-circle perimeter formulas

Sometimes, we need to calculate portions of a circle instead of a whole one. We can obtain the formulas for the perimeters of a half-circle and a quarter-circle by dividing the above equation by 2 and 4, respectively:

p_half = πr

p_quarter = πr/2

If you want to use the circle perimeter calculator to find the circumference of a circle, follow these steps:

1. Determine the radius of your circle. For example, let’s suppose it’s 7 cm.

2. Input the radius in the calculator, and you’ll know the circle’s circumference. The result should be 43.982 cm.

3. To double-check your result, enter the radius in the circle perimeter formula:

   p = 2 × π × (7 cm) = 43.982 cm

Now that you know how to find the perimeter of a circle, don’t forget this calculator is not our only tool for dealing with circular objects. We’re hopeful that the calculators below will help you with your day-to-day circular problems:

• Circle calc: find c, d, a, r;
• Circle measurements calculator;
• Circle formula calculator;
• Radius of a circle calculator;
• Circle length calculator;
• Circumference to diameter;
• Diameter of a circle calculator;
• Circumference and area of a circle calculator;
• Square footage of a circle calculator; and
• Square inches of a circle calculator.