Screen Size Calculator
Calculate screen width and height from diagonal and aspect ratio.
This screen size calculator finds a screen's actual width and height dimensions from its advertised diagonal size and aspect ratio, since TVs, monitors, and phones are conventionally marketed by diagonal measurement alone.
Enter the diagonal size and aspect ratio, and the calculator returns the screen's width and height.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| 55-inch diagonal, 16:9 aspect ratio | ≈47.9 in wide × 27.0 in tall | √(16² + 9²) = √337 ≈ 18.36. Width = 55 × (16 ÷ 18.36) ≈ 47.9 in. Height = 55 × (9 ÷ 18.36) ≈ 27.0 in. |
| 34-inch diagonal, 21:9 ultrawide ratio | ≈31.2 in wide × 13.4 in tall | √(21² + 9²) = √522 ≈ 22.85. Width = 34 × (21 ÷ 22.85) ≈ 31.2 in. Height = 34 × (9 ÷ 22.85) ≈ 13.4 in - noticeably shorter than a 16:9 screen at a similar diagonal. |
The Screen Dimension Formula
Using the Pythagorean theorem: width = diagonal x (ratio width / sqrt(ratio width^2 + ratio height^2)), and height = diagonal x (ratio height / sqrt(ratio width^2 + ratio height^2)). This treats the diagonal as the hypotenuse of a right triangle formed by the screen's width and height.
Why the Same Diagonal Can Look Different
Two screens with the same diagonal measurement but different aspect ratios (like 16:9 versus 21:9 ultrawide) have noticeably different actual width and height - a wider aspect ratio at the same diagonal is generally shorter in height, which matters when comparing viewing area, not just the marketed diagonal number.
How to Use the Screen Size Calculator
- Open the Screen Size Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the screen size calculator works.
Frequently Asked Questions
How do you calculate screen width and height from diagonal size?
Use the Pythagorean theorem with the aspect ratio: width = diagonal x (ratio width / sqrt(ratio width² + ratio height²)), and similarly for height using the ratio height.
Why do two TVs with the same diagonal size look different?
Different aspect ratios (like standard 16:9 versus ultrawide 21:9) distribute the same diagonal measurement differently between width and height, so the actual screen dimensions and viewing area differ even at the same diagonal size.
What is the most common screen aspect ratio?
16:9 is the most common aspect ratio for TVs, monitors, and many phone/tablet screens today, though ultrawide (21:9) and other ratios are also used, especially for specialized monitors and cinema formats.
How do I use this screen size calculator?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the Screen Size Calculator calculate?
Calculate screen width and height from diagonal and aspect ratio. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this screen size use?
The formula is: width = diagonal * ratio width / sqrt(rw^2 + rh^2). This formula is a direct application of the Pythagorean theorem, treating a screen's diagonal as the hypotenuse of a right triangle formed by its width and height - the industry convention of marketing screens by diagonal measurement alone dates to early television manufacturing in the mid-20th century, when it became the simplest single number to advertise a screen's size.
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Last updated: September 27, 2026.