Circumference Calculator
With diameter 10 ft, circumference comes to 31.416 ft — circumference. It is reached in 5 steps, the last of which is pi * 10, and each one is printed on the page with its numbers filled in. The formula is the one published by Wolfram MathWorld, not an approximation fitted to it.
Circumference of a circle from its diameter or the other way round, with the radius, the area and the arc of one degree shown alongside.
Formula and sources checked · How we check
Diameter 10 ft
31.416 ft
Circumference for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.
It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.
- Radius
10 / 25 ft- Circumference
pi * 1031.416 ft- Area enclosed
pi * pow(5, 2)78.54 sq ft- Arc length of one degree
31.415927 / 3600.087 ft- Circumference in inches
31.415927 * 12376.991 in
Worked example
A 10 ft circle measures 31.416 ft around and encloses 78.54 sq ft. One degree of that arc is 0.087 ft, or just over an inch — which is how much a mark moves for each degree you are out when laying out a curve.
How to work it out yourself
- 1.Measure straight across the widest point for the diameter.
- 2.Multiply by π. That is the circumference; nothing else is needed.
- 3.To go the other way, divide a measured circumference by π to recover the diameter.
- 4.For the area, halve the diameter and multiply π by that squared.
The formula
- Radius
10 / 2 - Circumference
pi * 10 - Area enclosed
pi * pow(5, 2) - Arc length of one degree
31.415927 / 360 - Circumference in inches
31.415927 * 12
Source: Wolfram MathWorld — circumference, NIST Digital Library of Mathematical Functions
Questions people actually ask
- How do I get the diameter from a tape around the object?
- Divide the measured circumference by π. A 31.4 ft tape reading is a 10 ft diameter, and this is the reliable way to size a tree or a tank you cannot measure across.
- Is π ever exactly 22/7?
- No. 22/7 is 3.142857, which is high by about 0.04%. It is close enough for a rough layout and wrong for anything machined.
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