Geometry & Measurement Calculators
Diagonal Calculator
Find the diagonal of a square, rectangle or rectangular box.
Loading tool…
What is Diagonal?
A diagonal is a straight line joining two non-adjacent corners. In a rectangle it is √(l² + w²); in a box it extends that to three dimensions.
How it works
We apply the Pythagorean theorem in two or three dimensions depending on the shape you choose.
- 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.