Find a screen’s diagonal size — the number manufacturers quote as “screen size” — from its width and height.
How it works
The diagonal is found with the Pythagorean theorem: diagonal = √(width² + height²). A screen 13.6 inches wide and 7.65 inches tall has a diagonal of about 15.6 inches.
What this does not include
This calculates diagonal size from measured width and height. It doesn’t derive width and height from an aspect ratio and a diagonal — that’s the reverse calculation, needing the aspect ratio as an additional input.
How to use this calculator
- Enter the screen’s width.
- Enter the screen’s height.
A worked example
A screen 13.6 × 7.65 inches: diagonal = √(13.6²+7.65²) = 15.6039 inches.
A 3 × 4 rectangle (scaled units): diagonal = 5 — the classic 3-4-5 right triangle.
What the variables mean
| Variable | Meaning |
|---|---|
| Width, height | The screen’s visible dimensions |
Edge cases worth knowing
Screen size is always advertised as the diagonal measurement, not width or height alone — which is why two screens with the same diagonal can have noticeably different actual widths if their aspect ratios differ.
A width of zero makes the diagonal calculation meaningless, so the calculator declines to show a result for that input.
Why do manufacturers quote diagonal size instead of width and height?
A single diagonal number is an easy shorthand for overall screen area, though it can be misleading when comparing screens with different aspect ratios — two screens with the same diagonal can have noticeably different actual widths.
Does this work for any aspect ratio?
Yes — the Pythagorean relationship between width, height, and diagonal holds regardless of aspect ratio, since it’s simply the geometry of a rectangle.
Should I measure the screen or the whole device including the bezel?
The screen itself — manufacturer-quoted sizes refer to the visible display area, not the outer casing or bezel.
