---
title: Math.PI
slug: Web/JavaScript/Reference/Global_Objects/Math/PI
translation_of: Web/JavaScript/Reference/Global_Objects/Math/PI
---
<div>{{JSRef("Global_Objects", "Math")}}</div>

<h2 id="Summary">概述</h2>

<p><code><strong>Math.PI</strong></code> 表示一个圆的周长与直径的比例，约为 3.14159：</p>

<p><math><semantics><mrow><mstyle mathvariant="monospace"><mi>Math.PI</mi></mstyle><mo>=</mo><mi>π</mi><mo>≈</mo><mn>3.14159</mn></mrow><annotation encoding="TeX">\mathtt{\mi{Math.PI}} = \pi \approx 3.14159</annotation></semantics></math></p>

<div>{{js_property_attributes(0,0,0)}}</div>

<h2 id="Description">描述</h2>

<p>由于 <code>PI</code> 是 <code>Math</code> 的静态属性，所以应该像这样使用：<code>Math.PI</code>，而不是作为你创建的 <code>Math</code> 实例的属性（<code>Math</code> 不是构造函数）。</p>

<h2 id="Examples">示例</h2>

<h3 id="Example:_Using_PI">使用 <code>Math.PI</code></h3>

<p>下面的函数使用 Math.PI 计算给定半径的圆周长：</p>

<pre class="brush:js">function calculateCircumference (radius) {
  return 2 * Math.PI * radius;
}

calculateCircumference(1);  // 6.283185307179586</pre>

<h2 id="规范">规范</h2>

<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">规范版本</th>
   <th scope="col">规范状态</th>
   <th scope="col">注解</th>
  </tr>
  <tr>
   <td>ECMAScript 1st Edition. Implemented in JavaScript 1.0</td>
   <td>Standard</td>
   <td>Initial definition.</td>
  </tr>
  <tr>
   <td>{{SpecName('ES5.1', '#sec-15.8.1.6', 'Math.PI')}}</td>
   <td>{{Spec2('ES5.1')}}</td>
   <td> </td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-math.pi', 'Math.PI')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td> </td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

{{Compat}}

<h2 id="See_also">相关链接</h2>

<ul>
 <li>The {{jsxref("Global_Objects/Math", "Math")}} object it belongs to.</li>
</ul>