Geometry
Circumference from the radius
The standard form. Double the radius and multiply by pi.
The Formula
C = 2 x pi x r
The standard form. Double the radius and multiply by pi.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| C | Circumference | metres | Distance around the circle. |
| r | Radius | metres | Centre to edge distance. |
What Each Symbol Means
Cmetres
Circumference
Distance around the circle.
rmetres
Radius
Centre to edge distance.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate the circumference of a circle page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate The Circumference Of A Circle, filed under Math. Every number the guide produces comes from substituting into this one line.