▭ 矩形计算器Rectangle Calculator
由长和宽计算矩形面积、周长、对角线和对角线夹角；也可由面积/周长加一条边反求。Area, perimeter, diagonal and diagonal angle of a rectangle from length and width, or solve from area/perimeter and one side.
使用说明与常见问题How-to & FAQ
「矩形计算器」是什么？What is the Rectangle Calculator tool?
由长和宽计算矩形面积、周长、对角线和对角线夹角；也可由面积/周长加一条边反求。Area, perimeter, diagonal and diagonal angle of a rectangle from length and width, or solve from area/perimeter and one side.
如何使用「矩形计算器」？How do I use the Rectangle Calculator tool?
在「矩形计算器」中，填写「已知」、「长 L」、「宽 W」、「面积 / 周长 / 对角线」等参数，结果会随输入实时计算并显示在下方。In the Rectangle Calculator: Fill in "Given", "Length L", "Width W", "Area / perimeter / diagonal"; results are recalculated instantly as you type.
计算精度如何？How precise are the results?
「矩形计算器」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 Rectangle Calculator uses double-precision floating point (about 15–16 significant digits); very large or very small values may lose precision.
「矩形计算器」免费吗？需要注册吗？Is the Rectangle Calculator free? Do I need an account?
「矩形计算器」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 Rectangle 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.