◓ 半圆面积计算器Area of a Semicircle Calculator
已知半径、直径、面积或周长中的任意一个，求半圆的面积 πr²/2、弧长 πr、周长（弧长 + 直径）以及形心到直径的距离 4r/(3π)。Given a semicircle's radius, diameter, area or perimeter, find its area πr²/2, arc length πr, perimeter (arc + diameter) and the distance from the diameter to its centroid, 4r/(3π).
使用说明与常见问题How-to & FAQ
「半圆面积计算器」是什么？What is the Area of a Semicircle Calculator tool?
已知半径、直径、面积或周长中的任意一个，求半圆的面积 πr²/2、弧长 πr、周长（弧长 + 直径）以及形心到直径的距离 4r/(3π)。Given a semicircle's radius, diameter, area or perimeter, find its area πr²/2, arc length πr, perimeter (arc + diameter) and the distance from the diameter to its centroid, 4r/(3π).
如何使用「半圆面积计算器」？How do I use the Area of a Semicircle Calculator tool?
在「半圆面积计算器」中，填写「已知」、「数值」、「单位（可选，如 cm）」等参数，结果会随输入实时计算并显示在下方。In the Area of a Semicircle Calculator: Fill in "Given", "Value", "Unit (optional, e.g. cm)"; results are recalculated instantly as you type.
半圆面积公式？What is the area of a semicircle?
半圆面积 = πr² ÷ 2，即同半径整圆面积的一半；用直径 d 表示为 πd² ÷ 8。Area = πr² ÷ 2, half a full circle of the same radius; with the diameter d it is πd² ÷ 8.
半圆周长包括直径吗？Does the perimeter include the diameter?
包括。半圆的周长 = 弧长 πr + 直径 2r = (π + 2)r。如果只要弯曲部分，看「弧长」一项。Yes: perimeter = arc πr + diameter 2r = (π + 2)r. For the curved part only, use the arc length.
计算精度如何？How precise are the results?
「半圆面积计算器」使用 JavaScript 双精度浮点数（约 15–16 位有效数字）；极大或极小的数值可能存在精度误差。The Area of a Semicircle Calculator uses double-precision floating point (about 15–16 significant digits); very large or very small values may lose precision.
「半圆面积计算器」免费吗？需要注册吗？Is the Area of a Semicircle Calculator free? Do I need an account?
「半圆面积计算器」完全免费，无需注册或安装，打开网页即可使用，手机和电脑都能用；输入的内容只在你的浏览器本地处理。The Area of a Semicircle Calculator is completely free with no sign-up or install and works on phones and desktops; what you enter is processed only in your browser.