Screen sizes are almost always advertised as a single diagonal measurement — “55-inch TV,” “27-inch monitor” — which doesn’t tell you the actual width and height you need for planning a desk, TV stand, or wall mount. This calculator converts a diagonal screen size and aspect ratio into physical width and height, so you know exactly how much space a screen will take up.
What the Result Means
The result gives you the screen’s actual width and height in inches (or centimeters), based on its diagonal measurement and aspect ratio. This is the number that actually matters for physical planning: whether a monitor fits on your desk, whether a TV fits in an entertainment unit, or how much wall space a mounted display needs — the diagonal figure alone doesn’t tell you any of that, since two screens with the same diagonal size but different aspect ratios can have noticeably different widths and heights.
For instance, an ultrawide monitor and a standard 16:9 monitor can share the same diagonal size on paper while looking completely different in person — the ultrawide is proportionally wider and shorter. Knowing the actual width and height ahead of time avoids the surprise of a screen that’s wider than expected or taller than your available space.
How This Calculator Works
The calculation relies on the Pythagorean theorem, since the diagonal, width, and height of a rectangular screen form a right triangle. Given the aspect ratio (width : height) and the diagonal length, the calculator first works out how many “ratio units” fit into the diagonal, then multiplies that by the width and height ratio values.
Formula: for an aspect ratio of a:b and diagonal d, the diagonal in ratio units is √(a² + b²). One ratio unit then equals d ÷ √(a² + b²). Width = a × (that unit), and height = b × (that unit).
Worked example: Take a 27-inch diagonal screen with a 16:9 aspect ratio. √(16² + 9²) = √(256 + 81) = √337 ≈ 18.36. One ratio unit = 27 ÷ 18.36 ≈ 1.47 inches. Width = 16 × 1.47 ≈ 23.6 inches. Height = 9 × 1.47 ≈ 13.3 inches. So a 27-inch 16:9 monitor is roughly 23.6 inches wide and 13.3 inches tall, not counting the bezel.
Important Limitations
This calculator gives you the panel’s active display area — the actual image surface — not the outer dimensions of the physical device. Bezels, stands, and enclosures add extra width and height beyond what’s calculated here, so if you’re checking whether a monitor fits in a tight space, add a reasonable margin for the frame and base. Manufacturer spec sheets usually list the exact outer dimensions if you need precise measurements for furniture or mounting.
Also double-check the aspect ratio you enter — it’s usually printed in the product specs, but some screens (especially ultrawide monitors) use less common ratios like 21:9 or 32:9 rather than the standard 16:9, and using the wrong ratio will throw off the width and height results.
Frequently Asked Questions
Why do two screens with the same diagonal size look different?
Because diagonal size alone doesn’t determine shape — aspect ratio does. A 34-inch ultrawide (21:9) and a 34-inch standard monitor (16:9, if such existed) would have the same diagonal measurement but very different width and height, since the ultrawide is stretched proportionally wider and shorter.
Does screen size include the bezel?
No. Advertised diagonal screen sizes refer to the visible display area only, not the bezel or outer casing. The width and height this calculator produces are for that same active display area — actual product dimensions will be somewhat larger once the bezel and frame are included.
How do I find my screen's aspect ratio?
It’s usually listed in the product spec sheet as two numbers separated by a colon, like 16:9 or 21:9. If you only know the resolution, you can find the aspect ratio using the Aspect Ratio Calculator, then plug that into this tool.
Is this useful for TVs as well as monitors?
Yes — the math is identical for TVs, monitors, laptop screens, and phone displays. Just make sure you’re using the correct diagonal size and aspect ratio for the specific screen you’re measuring.