Circle area
Circle area A = πr²: enter the radius to get the area plus circumference 2πr and diameter 2r; values are rounded to 6 decimals and a non-positive radius is rejected.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Result
One quantity per line, ready to copy.
Enter a radius to calculate
What this tool does
- Compute the area of a round panel, table top or plot and get the circumference for edging or fencing.
- Compare how the area grows with the radius — it scales with the square, so doubling the radius multiplies the area by four.
- Verify the formulas: area πr² and circumference 2πr.
Example
Input
2
Output
半径 2 的圆面积：12.566371 周长 2πr：12.566371 直径 2r：4 长度单位 u，面积 u²，体积 u³
At radius 1 the area is π ≈ 3.141593, the circumference 2π ≈ 6.283185 and the diameter 2 — all canonical.
Frequently asked questions
What if the radius is 0?
It reports an error instead of returning 0. A zero radius collapses the circle into a point — the formula still evaluates but the answer is meaningless, so non-positive input is rejected.
Do I get area and circumference together?
Yes. The result lists area, circumference and diameter, so you do not have to run a second calculation for cutting or estimating.
How precise is the output?
Six decimals throughout. π is irrational, so every decimal output is an approximation, and six decimals is plenty for engineering and everyday work.
Keywords：圆形面积Circle area圆circle几何计算geometry面积