Circle Calculator
A = πr² and C = 2πr. Click any i for detail.
Circle
Known
i
Known
Which measurement you have. |
|
|---|---|
Radius
i
r
Center to edge. |
|
Diameter
i
d
Across the circle. |
|
Circumference
i
C
Distance around. |
|
Area
i
A
πr². |
How to use this calculator
- Select whether you know radius, diameter, circumference, or area.
- Enter that measurement.
- Read all four circle values consistently.
- Keep units consistent (all cm or all in).
Results explained
All values derive from radius. π is used for circumference and area. Room flooring is usually rectangular square footage, not a circle.
Quick reference: circle
If r = 5, then d = 10, C ≈ 31.416, A ≈ 78.54 in the same units.
| Item | Detail |
|---|---|
| Diameter | d = 2r |
| Circumference | C = 2πr |
| Area | A = πr² |
| From area | r = √(A/π) |
Units stay whatever you typed; they are not converted.
How the estimate is built
d=2r; C=2πr; A=πr².
Example scenario
r = 5 → area 78.54 (π×25).
FAQ
Which value should I measure on site?
Radius is hard to measure directly; diameter or circumference is often easier.
Does π use 3.14?
The page uses a full-precision π constant, not 3.14.
Can this do semicircles?
Take half the full circle area or arc if you know the fraction.