Screen Size Calculator
Calculate the real width, height, area, and pixel density of any screen from its diagonal size and aspect ratio. Enter a diagonal in inches (like 27 inches) and a ratio (like 16:9) to get the exact physical width and height, the screen area in square inches, and — if you add the resolution — the pixels per inch (PPI). Perfect for comparing monitors, TVs, laptops, and phones, checking if a display fits a desk or wall, and judging how sharp a screen will look.
Add the pixel resolution to also calculate pixel density (PPI).
ToolsSoup's Screen Size Calculator turns a screen's diagonal measurement and aspect ratio into the real physical dimensions you actually care about: the width, the height, the total surface area, and the pixel density. Enter a diagonal in inches — say 27 — pick a ratio like 16:9, and instantly read how wide and tall the panel really is, plus its area in square inches. Add the pixel resolution and it also reports the PPI (pixels per inch) so you can judge how sharp the display will look. It's the fastest way to compare monitors, TVs, laptops, and phones, check whether a screen fits a desk, stand, or wall mount, and understand what a diagonal size really means. Everything runs in your browser: no uploads, no sign-up, and your numbers never leave your device.
What is a screen size calculator?
A screen size calculator works out a display's real width and height from two numbers manufacturers always give you: the diagonal size and the aspect ratio. Screens are advertised by their diagonal — a 27-inch monitor or a 65-inch TV — but the diagonal alone doesn't tell you how wide or tall the panel is. By combining the diagonal with the aspect ratio (16:9, 16:10, 4:3, and so on), the calculator splits that diagonal into its horizontal and vertical components using the Pythagorean theorem. The result is the actual width and height in inches, the screen area, and, when you supply the resolution, the pixel density that determines how crisp the image looks.
How to calculate screen width and height
Getting the real dimensions of a screen takes just a couple of inputs, and the results update as you type:
- Enter the diagonal size in inches (the number used to advertise the screen).
- Set the aspect ratio, or click a preset like 16:9 or 16:10.
- Read the calculated width, height, and area in the result panel.
- Optionally enter the horizontal and vertical pixel resolution to also get the pixel density (PPI).
- Copy the result to compare screens or check whether one fits your space.
The math behind screen dimensions
The diagonal of a screen forms the hypotenuse of a right triangle whose other two sides are the width and the height. If the aspect ratio is w:h, the diagonal length corresponds to the square root of (w² + h²). To find the real width, multiply the diagonal by w and divide by that square root; for the height, multiply the diagonal by h and divide by the same value. For a 27-inch 16:9 monitor that gives a width of about 23.53 inches and a height of about 13.24 inches. Multiply width by height for the area, and divide the diagonal pixel count by the diagonal inches to get pixels per inch.
What pixel density (PPI) tells you
Pixel density, measured in pixels per inch (PPI), describes how tightly packed the pixels are on a screen. A higher PPI means finer detail and smoother text at the same viewing distance. To calculate it, the tool takes the diagonal pixel count — the square root of (horizontal² + vertical²) — and divides it by the diagonal in inches. A 27-inch 2560 × 1440 monitor lands around 109 PPI, while a 24-inch 1920 × 1080 display is about 92 PPI, and modern phones often exceed 400 PPI. Comparing PPI across screens helps you decide whether a display will look sharp at the distance you'll actually use it.
Why use this screen size calculator?
- Converts a diagonal size and aspect ratio into real width and height in inches.
- Shows the total screen area so you can compare how much surface different sizes give you.
- Calculates pixel density (PPI) when you add the resolution, to judge sharpness.
- Includes presets for 16:9, 16:10, 4:3, 21:9, 3:2, and 1:1 and updates live as you type.
- Runs entirely in your browser — free, no ads, and your numbers never leave your device.
Frequently asked questions
How do I calculate the width and height of a screen from the diagonal?
Use the aspect ratio together with the diagonal. For a ratio of w:h, the width is the diagonal times w divided by the square root of (w² + h²), and the height is the diagonal times h divided by the same value. This calculator does it for you — just enter the diagonal and ratio.
What are the real dimensions of a 27-inch 16:9 monitor?
A 27-inch 16:9 screen is about 23.53 inches wide and 13.24 inches tall, with an area of roughly 311 square inches. Enter 27 as the diagonal and 16:9 as the ratio above to confirm it.
What aspect ratio should I use?
Most modern monitors and TVs are 16:9. Many productivity and laptop screens use 16:10, ultrawide monitors use 21:9, older displays and tablets often use 4:3, and many photography screens and laptops use 3:2. Pick the ratio that matches your screen, or use a preset button.
How is pixel density (PPI) calculated?
PPI is the diagonal pixel count divided by the diagonal size in inches. The diagonal pixel count is the square root of (horizontal pixels² + vertical pixels²). Add the resolution to the calculator and it returns the PPI automatically — a higher number means a sharper image.
Why is a screen's diagonal larger than its width?
The diagonal runs corner to corner, so it's always longer than either side. A 27-inch screen is only about 23.5 inches wide because that 27 inches is the slanted distance across the panel, not its width. That's why two screens with the same diagonal can look different depending on their aspect ratio.