Diameter Calculator
The diameter is the width of a circle through its center. Enter the circumference, the radius or the area and get the diameter — handy for sizing pipes, columns, pots and anything you can wrap a tape around but cannot measure across.
- Radius
- 7.0028 in
- Circumference
- 44 in
- Area
- 154.062 in²
Saved setups
Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.
Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Choose what you know: circumference, radius or area.
- Enter the value and its unit.
- Read the diameter in the unit you need.
Worked examples
A column 44 inches around: 14.006 in across, which is 0.3557 m
- Diameter
- 14.0056 in
A circle with an area of 100 in²: 11.284 in across (0.2866 m)
- Diameter
- 11.2838 in
- Radius
- 5.6419 in
A circle 10 m around
- Diameter
- 3.1831 m
Pipe sizes are not exact diameters
Dividing a measured circumference by π gives the true outside diameter. Nominal pipe sizes are trade names that match neither the inside nor the outside diameter exactly — a US “1-inch” steel pipe measures 1.315 inches across the outside — so compare your result with a pipe size chart.
Questions people ask
What is the diameter of a circle with a circumference of 44 inches?
44 ÷ π = 14.01 inches.
What is the diameter of a circle with an area of 100 square inches?
2 × √(100 ÷ π) = 11.28 inches.
How do I measure the diameter of something round?
Measure straight across the widest point, or wrap a flexible tape around it and divide that circumference by 3.1416.