Screen Size Calculator
Find screen dimensions from diagonal and ratio.
16 for 16:9
9 for 16:9
Results update as you type.
How it works
Screens are advertised by their diagonal measurement, but the actual width and height depend on the aspect ratio, and this calculator finds them. You enter the diagonal size and the aspect ratio (like 16:9), and it returns the screen's width, height, and area in inches. The calculation uses the Pythagorean theorem: since the diagonal, width, and height form a right triangle, the width and height can be recovered from the diagonal and the ratio between them. This matters because two screens with the same diagonal can have different shapes and areas — a 27-inch 16:9 monitor and a 27-inch 21:9 ultrawide have very different widths, heights, and total viewing areas despite the identical diagonal number. Knowing the real dimensions helps you check whether a TV will fit a wall space or media console, compare the actual screen area of different models, or verify that a monitor suits your desk. It also reveals that ultrawide and taller-ratio screens of the same diagonal have less area than a 16:9, since a square-ish shape maximizes area for a given diagonal. The area figure lets you compare true screen real estate across different aspect ratios. Enter the diagonal and aspect ratio to find the dimensions.
Width = diagonal × w ÷ √(w² + h²); height = diagonal × h ÷ √(w² + h²)
Screens are measured by their diagonal, but the width and height depend on the aspect ratio. Using the Pythagorean theorem, the width is the diagonal times the ratio width divided by the square root of the sum of the squared ratio terms, and the height uses the ratio height similarly.
Source:Geometry (Pythagorean theorem)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter diagonal size.
- 2
Adjust the options
Adjust aspect ratio width and aspect ratio height if they apply — sensible defaults are already set.
- 3
Read your result
Width updates instantly as you type — no button to press.
Frequently asked questions
How do you find screen width and height from the diagonal?
Use the aspect ratio and the Pythagorean theorem. The width equals the diagonal times the ratio width divided by the square root of the ratio width squared plus the ratio height squared, and the height uses the ratio height the same way. For a 27-inch 16:9 screen, that gives about 23.5 inches wide and 13.2 inches tall.
Why do same-diagonal screens differ in size?
Because the diagonal alone does not determine width and height — the aspect ratio does. A 27-inch 16:9 monitor and a 27-inch 21:9 ultrawide share the same diagonal but have different widths, heights, and areas. The wider the ratio, the wider and shorter the screen, so always consider the aspect ratio, not just the diagonal, when comparing.
Which aspect ratio gives the most screen area?
For a fixed diagonal, a more square shape gives more area. Among common ratios, 4:3 has more area than 16:9, which in turn has more than 21:9 ultrawide, all at the same diagonal. So an ultrawide monitor labeled the same inches as a 16:9 actually has less total screen area, a trade-off for its extra width.
How do I check if a TV will fit my space?
Calculate the TV's actual width and height from its diagonal and 16:9 ratio, then add a few inches for the bezel and stand, and compare against your wall space or media console dimensions. The advertised diagonal alone can mislead, so using the real width and height ensures the TV physically fits where you plan to put it.
What is a common screen aspect ratio?
16:9 is the standard for most TVs, monitors, and laptops. Ultrawide monitors use 21:9, some productivity monitors use 16:10, older screens used 4:3, and phones vary widely. Enter your screen's aspect ratio into the calculator; if you are unsure, 16:9 is the safe default for modern TVs and most computer displays.