Convert between the metric units everyone uses — millimeters, centimeters, meters and kilometers — and the imperial units still common in the United States: inches, feet, yards and miles. Type a value, pick the two units, and every other unit in the list updates instantly.
The conversion is exact and happens entirely in your browser: one inch is exactly 25.4 mm by international agreement, and every other factor on this page is derived from the definitions below. Nothing you type is sent anywhere.
Frequently asked questions
How many feet are in a mile?
Exactly 5,280 feet — or 1,609.344 meters, since the international mile is defined as 1,609.344 mm × 1000.
Is 1 inch exactly 2.54 cm?
Yes. Since 1959 the inch has been defined as exactly 25.4 mm, so 1 inch = 2.54 cm with no rounding.
Do my inputs leave my computer?
No. The converter is plain JavaScript running in your browser — it works offline once the page has loaded.
中文说明
在毫米、厘米、米、千米等公制单位与英寸、英尺、码、英里等英制单位之间自由换算。输入数值后所有单位实时同步更新，无需点击任何按钮。
换算完全在浏览器本地完成，精确无误差：1 英寸按国际标准精确等于 25.4 毫米，其余系数均由此推导。你输入的内容不会被上传到任何服务器。
常见问题
一英里等于多少英尺？
精确值是 5280 英尺，即 1609.344 米——国际英里的定义就是 1609.344 毫米 × 1000。
1 英寸正好是 2.54 厘米吗？
是的。自 1959 年起英寸被定义为精确的 25.4 毫米，因此 1 英寸 = 2.54 厘米没有任何舍入误差。
我输入的数据会被上传吗？
不会。换算由浏览器中的 JavaScript 本地完成，页面加载后即使断网也能继续使用。