Cylinder Diameter Calculator
Find a cylinder's diameter from a measured circumference (wrap a tape around it) or from the known radius. Enter one value and the calculator derives diameter, radius, circumference and base area.
units
units
d = C ÷ π (from measured circumference)
- 1
Measured circumference
31.416 - 2
π
3.141593 - 3
Diameter d = C ÷ π
31.416 ÷ π = 10
How does this calculator work?
Cylinder diameter: d = C ÷ π when you measure the circumference around the outside, or d = 2 × r when you know the radius. Dividing the circumference by π ≈ 3.14159 is the practical way to measure pipes and round objects without callipers.
Formula
How this is calculated
The diameter of a circular cross-section is the chord through the centre — twice the radius. If you can wrap a flexible tape measure around a cylindrical object and read off the circumference C, the diameter follows immediately from d = C ÷ π ≈ C ÷ 3.14159. This is the standard method for measuring pipes, tree trunks, columns, or any cylinder you cannot measure across directly.
If you already know the radius, the diameter is simply d = 2r, and the circumference is C = πd = 2πr. Both paths are supported: enter the circumference in the top field (leave radius blank), or enter the radius in the lower field (leave circumference blank). If both are filled, circumference takes priority.
All results are in the same unit you enter. There is no built-in conversion — use consistent units (all cm, all inches, etc.) throughout.
Frequently asked questions
Wrap a flexible tape, string, or strip of paper around the cylinder and measure its circumference C. Then divide by π: d = C ÷ 3.14159. This works for pipes, posts, tree trunks, or any round object you can't span directly.
The diameter is exactly twice the radius: d = 2r, or r = d ÷ 2. The diameter is the longest chord of a circle and passes through the centre.
Not directly in this calculator — it does not convert units. First convert the circumference to centimetres (1 inch = 2.54 cm), then enter the converted value to get the diameter in centimetres.
Also known as
TG we-Calculate Editorial Team. (2026). Cylinder Diameter Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/cylinder-diameter-calculator
TG we-Calculate Editorial Team. "Cylinder Diameter Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/cylinder-diameter-calculator.
TG we-Calculate Editorial Team, "Cylinder Diameter Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/cylinder-diameter-calculator
@misc{wecalculate_cylinder_diameter_calculator, title = {Cylinder Diameter Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/cylinder-diameter-calculator}}, year = {2026}, note = {TG we-Calculate} }
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