⭕ 周长转直径Circumference to Diameter Calculator
圆：d = C / π，也可由直径求周长。可设置「已知」、「数值」。Circle: d = C / π; also C from diameter. Settings: Given, Value.
使用说明与常见问题How-to & FAQ
「周长转直径」是什么？What is the Circumference to Diameter Calculator tool?
圆：d = C / π，也可由直径求周长。可设置「已知」、「数值」。Circle: d = C / π; also C from diameter. Settings: Given, Value.
如何使用「周长转直径」？How do I use the Circumference to Diameter Calculator tool?
在「周长转直径」中，填写「已知」、「数值」等参数，结果会随输入实时计算并显示在下方。In the Circumference to Diameter Calculator: Fill in "Given", "Value"; results are recalculated instantly as you type.
π 取多少位？How precise is π?
使用 JavaScript 内置的 Math.PI = 3.141592653589793，精度约 15 到 16 位有效数字，远超日常测量的需要。直径 d = 周长 ÷ π，周长 = π × d。It uses JavaScript's Math.PI = 3.141592653589793, about 15 to 16 significant digits, far more than any measurement needs. Diameter d = circumference ÷ π, and circumference = π × d.
能举个计算实例吗？Can you show a worked example?
例如在「周长转直径」中填 已知 = 周长，数值 = 6.283185307179586，结果区显示：直径：2；半径：1；面积：3.141593For example, entering Given = Circumference, Value = 6.283185307179586 in the Circumference to Diameter Calculator gives: Diameter: 2; Radius: 1; Area: 3.141593
哪些输入会被检查？Which inputs are validated?
「周长转直径」会检查这些输入——「数值」：必须填写，须大于 0；绝对值超过 10¹⁵ 的数也会被拒绝。不符合时结果区显示具体提示，不会给出数字。The Circumference to Diameter Calculator checks its inputs — "Value": required, must be greater than 0; numbers above 10¹⁵ in absolute value are rejected too. When a value fails, the result area names the problem instead of showing a number.
有哪些选项可以调整？What options can I adjust?
「周长转直径」的设置：「已知」可选 周长、直径（默认 周长）；「数值」默认 31.415926。每次生成结果都按当前设置处理。Settings in the Circumference to Diameter Calculator — "Given": Circumference, Diameter (default Circumference); "Value" default 31.415926. The result always uses the current settings.
计算精度如何？How precise are the results?
「周长转直径」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 Circumference to Diameter Calculator uses double-precision floating point (about 15–16 significant digits); very large or very small values may lose precision.
「周长转直径」免费吗？需要注册吗？Is the Circumference to Diameter Calculator free? Do I need an account?
「周长转直径」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 Circumference to Diameter 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.