To find the diameter of a circle from its circumference, divide the circumference by pi (which is roughly 3.14159). For example, if a circle has a circumference of 31.42 inches, dividing 31.42 by 3.14159 gives a diameter of 10 inches. This simple calculation works for any unit of measurement, including inches, feet, centimeters, and meters.
The distance around the circle
Quick Examples:
10.0000
in
3.1831
in
1.5915
in
7.9577
in²
C = π × d = π × 0.0809 = 0.2540 inC = 2 × π × r = 2 × π × 0.0404 = 0.2540 ind = C / π = 0.2540 / π = 0.0809 inr = C / (2π) = 0.2540 / (2π) = 0.0404 inA = π × r² = π × 0.0404² = 0.0051 in²A = π × (d/2)² = π × (0.0809/2)² = 0.0051 in²The formula to find diameter from circumference is:
d = C / π
In this formula, d represents the diameter, C represents the circumference, and π represents the mathematical constant pi (approximately 3.14159).
Because pi is the ratio of a circle's perimeter to its width, dividing the outer measurement by pi always reveals the distance directly across the center. If you need to convert in the opposite direction, you can use a diameter to circumference calculator to multiply the width by pi instead.
Converting circumference into diameter requires three simple steps:
Imagine you wrap a flexible tape measure around a large round pipe and get a length of 50 centimeters.
Step 1: C = 50 cm
Step 2: π ≈ 3.14159
Step 3: d = 50 / 3.14159
Result: d = 15.915 cm
If you need the distance from the center point to the outer edge rather than the full width, you can check our radius calculator to divide your diameter result by two.
If you already know the diameter and need the outer distance around the circle, rearrange the formula to solve for C:
C = π × d
Multiply the diameter by 3.14159. For instance, a wheel with a 24-inch diameter has a total circumference of roughly 75.4 inches (24 × 3.14159). For space-related geometry tasks involving two dimensional surfaces, working with a circle area calculator allows you to solve for total interior surface area alongside edge measurements.
Here are common circumference measurements converted directly to diameter using the standard pi approximation:
| Circumference (C) | Diameter (d) | Radius (r) |
|---|---|---|
| 3.14 units | 1.00 unit | 0.50 units |
| 10.00 units | 3.18 units | 1.59 units |
| 12.57 units | 4.00 units | 2.00 units |
| 25.00 units | 7.96 units | 3.98 units |
| 31.42 units | 10.00 units | 5.00 units |
| 50.00 units | 15.92 units | 7.96 units |
| 100.00 units | 31.83 units | 15.92 units |
Pi is a mathematical constant equal to roughly 3.14159. It represents the exact ratio of any circle's circumference to its diameter. Every circle, regardless of size, maintains this exact ratio.
Yes. The diameter is always twice the radius (d = 2r). If you know the radius, multiply it by 2 to get the diameter.
Wrap a soft, flexible tape measure around the widest part of the object. If you only have a stiff ruler, wrap a string around the object, mark where it overlaps, and measure the flat string against your ruler.
Dividing 10 inches by 3.14159 gives a diameter of approximately 3.18 inches.
Yes. Circumference is simply the specific term used for the perimeter of a circular shape.