Geometry & Measurement Calculators
Rectangle Diagonal Calculator
Find the diagonal of a rectangle from its length and width.
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What is Rectangle Diagonal?
A rectangle's diagonal is the hypotenuse of the right triangle formed by its length and width, so it follows directly from the Pythagorean theorem: d = √(l² + w²).
How it works
We square the length and width, add them, and take the square root — the same calculation as any right-triangle hypotenuse, with the area and perimeter shown for context.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.