How to Use
- 1.
Choose whether to convert circumference to diameter or diameter to circumference.
- 2.
Enter a positive measurement.
- 3.
Select the measurement unit.
- 4.
Read the calculated diameter or circumference, radius, and area.
Features
Convert circumference to diameter with d = C ÷ π
Reverse mode calculates circumference from diameter
Displays radius and circle area
Supports millimeters, centimeters, meters, inches, feet, and yards
Instant browser-based results
Copy the calculated value
Frequently Asked Questions
How do I calculate diameter from circumference?+
Divide the circumference by pi (π ≈ 3.14159). The formula is d = C ÷ π.
What is the formula for circumference from diameter?+
Multiply the diameter by pi: C = π × d.
What is the diameter if the circumference is 25 inches?+
25 ÷ π is approximately 7.96 inches. The calculator keeps the selected unit for its linear measurements.
Does this calculator convert measurement units?+
Choose a unit for your input from the selector. The result is expressed in that same unit; the tool does not convert a value between unit systems.
How are radius and area calculated?+
Radius is half the diameter. Area is π times radius squared and is displayed in square units.
Does this work for oval or irregular shapes?+
No. These formulas describe a perfect circle. An oval or irregular object does not have one circle diameter that can be derived from its perimeter using this formula.
About this tool
Free Circumference to Diameter Calculator
## Circumference to Diameter Calculator
Use this circumference to diameter calculator to find a circle's diameter from its circumference. Enter a positive measurement, choose a unit, and get the diameter, radius, and area. Switch modes to calculate circumference from diameter.
### How to Calculate Diameter from Circumference
A circle's circumference and diameter are connected by pi (π). To find diameter from circumference, divide the circumference by π: **d = C ÷ π**. For example, if a circle measures 25 inches around, its diameter is about 7.96 inches.
To calculate circumference from diameter, multiply the diameter by π: **C = π × d**. Radius is half the diameter, and circle area is π multiplied by radius squared. Results use the same unit you selected; area is shown in that unit squared.
### When to Use This Calculator
This calculator can help with classroom geometry, checking a circular object's dimensions, or converting between common circle measurements. It assumes a perfect circle and does not account for measurement error or irregular shapes.
### Formula
- Diameter: d = C / π - Circumference: C = πd - Radius: r = d / 2 - Area: A = πr²
The calculation runs in your browser. For rectangular room or floor measurements, use the Square Footage Calculator.
Measuring a circular room or surface? Use the Square Footage Calculator for room area, or browse more Calculators.