Circumference to Diameter Calculator
Know the circumference but need the diameter? Enter C and get d = C ÷ π instantly, along with the radius and enclosed area.
d = C ÷ π
- 1
Circumference (input)
31.4159 - 2
Diameter
31.4159 ÷ π = 9.999992Rearranging C = πd gives d = C ÷ π.
How does this calculator work?
Diameter equals circumference divided by π: d = C/π. For C = 31.4159, d = 10.000. The radius is half the diameter (r = C/2π) and area is πr². Most useful when you can wrap a tape around a circular object but cannot measure straight across it.
Formula
How this is calculated
The circumference formula is C = πd. Rearranging to solve for diameter gives d = C/π. Because π is the universal ratio of circumference to diameter for any circle, dividing by π precisely reverses the formula.
Once the diameter is found, the radius is simply r = d/2 = C/(2π), and the area follows from A = πr². The calculation is exact in principle — π is irrational, so the decimal representation never terminates — but the calculator gives up to 6 significant figures using Math.PI ≈ 3.141592653589793.
A common real-world use is measuring the outer perimeter of a round pipe, tree trunk, or wheel with a flexible tape measure, then computing the diameter when measuring straight across is impractical. Wrapping a tape around any circular object gives you the circumference; this calculator converts that to the diameter you actually need.
Frequently asked questions
d = C ÷ π. For example, a circumference of 62.83 gives d = 62.83 / 3.14159 ≈ 20.
d = 100 / π ≈ 31.831. The radius is half that: r ≈ 15.916.
Because the circumference formula is C = πd, and rearranging gives d = C/π. The constant π is defined as the ratio C/d for any circle — it is the same for every circle, which makes the conversion exact.
TG we-Calculate Editorial Team. (2026). Circumference to Diameter Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/circumference-to-diameter-calculator
TG we-Calculate Editorial Team. "Circumference to Diameter Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/circumference-to-diameter-calculator.
TG we-Calculate Editorial Team, "Circumference to Diameter Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/circumference-to-diameter-calculator
@misc{wecalculate_circumference_to_diameter_calculator, title = {Circumference to Diameter Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/circumference-to-diameter-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?