圆面积计算器
计算圆的面积、周长和直径。
Calculating the Area and Circumference of a Circle
概述
The area of a circle measures the space inside it, and the circumference measures the distance around it — both derived from the radius. This calculator finds them instantly from the radius, diameter, or circumference in your browser.
使用步骤
- 1
Enter a known measurement
Provide the radius, diameter, or circumference.
- 2
Calculate
The tool derives the radius and computes area and circumference.
- 3
Read the results
Both area and circumference are shown together.
工作原理
Area = π × r², and circumference = 2 × π × r, where r is the radius and π is about 3.14159. If you know the diameter instead, the radius is half of it; if you know the circumference, the radius is circumference ÷ (2π). The tool accepts whichever measurement you have and computes the rest.
什么时候用
Working out material needed for a circular area like a garden bed or table. Solving a geometry problem. Finding the circumference for fencing or trim around a round object.
常见问题
Area = π × radius². For a radius of 5, that is π × 25 ≈ 78.54 square units.