Follow a worked example.
Every example below can be loaded using its calculator’s Reset example button. Inputs use centimetres, square centimetres or cubic centimetres as labelled, while angles use degrees.
From a radius
Given: Radius r = 5.
A = πr²; C = 2πr
| Measurement | Calculated value |
|---|---|
| Radius | 5 cm |
| Diameter | 10 cm |
| Area | 78.539816 cm² |
| Circumference | 31.415927 cm |
From a diameter
Given: Diameter d = 10.
r = d/2
| Measurement | Calculated value |
|---|---|
| Radius | 5 cm |
| Diameter | 10 cm |
| Area | 78.539816 cm² |
| Circumference | 31.415927 cm |
Find radius from area
Given: Area A = 78.5398163397.
r = √(A/π)
| Measurement | Calculated value |
|---|---|
| Radius | 5 cm |
| Diameter | 10 cm |
| Area | 78.539816 cm² |
| Circumference | 31.415927 cm |
Sector of a circle
Given: Radius r = 5; Central angle θ = 90.
Sector area = πr²θ/360; arc = 2πrθ/360
| Measurement | Calculated value |
|---|---|
| Sector area | 19.634954 cm² |
| Arc length | 7.8539816 cm |
| Sector boundary length | 17.853982 cm |
Check the answer’s dimensions
An area contains a product of two lengths, while volume contains three. A perimeter or radius is still a length. If your input measurements are mixed between metres and centimetres, convert them to a common unit first. A realistic-looking number can still be wrong if the units were inconsistent.