Screen Size Converter (Diagonal ↔ Width/Height)
Convert screen diagonal to width & height using aspect ratio—or calculate diagonal from width and height.
What the screen size converter does
The screen size converter turns a diagonal measurement into width and height for a given aspect ratio, or does the reverse and finds the diagonal from a known width and height. Enter the diagonal in inches and pick the aspect ratio, or enter width and height and leave the diagonal empty, then press Calculate. Screens are sold by their diagonal, so this is how you find out whether a monitor or TV will fit a desk, a cabinet or a wall.
The formulas
For an aspect ratio of w:h and diagonal d:
- width = d × w / √(w² + h²)
- height = d × h / √(w² + h²)
- diagonal from width and height: d = √(width² + height²)
For 16:9, √(16² + 9²) = 18.36, so width = 0.8716 × d and height = 0.4903 × d. A 27-inch 16:9 monitor is 23.5 by 13.2 inches (59.8 by 33.6 cm).
Common screen sizes
| Diagonal | Aspect | Width | Height | Typical device |
|---|---|---|---|---|
| 6.1 in | 19.5:9 | 5.54 in | 2.56 in | Smartphone |
| 13.3 in | 16:10 | 11.28 in | 7.05 in | Laptop |
| 24 in | 16:9 | 20.92 in | 11.77 in | Office monitor |
| 27 in | 16:9 | 23.53 in | 13.24 in | Desktop monitor |
| 34 in | 21:9 | 31.25 in | 13.39 in | Ultrawide monitor |
| 55 in | 16:9 | 47.94 in | 26.96 in | Living-room TV |
| 75 in | 16:9 | 65.37 in | 36.77 in | Large TV |
These are panel dimensions. Bezels add 0.2 to 1 inch per side, and stands add several inches of depth and height. Check the manufacturer’s outline drawing before cutting a shelf.
Aspect ratios available
| Ratio | Where it is used |
|---|---|
| 16:9 | TVs, most monitors, HD and 4K video |
| 4:3 | Older TVs and monitors, iPads, some projectors |
| 21:9 | Ultrawide monitors, cinema-style video |
| 3:2 | Surface laptops, many photo sensors |
| 1:1 | Square displays, signage, some instrument screens |
16:10 laptop panels are close to 3:2 in shape; for a precise answer enter the panel’s width and height instead of using a preset.
Comparing screens of different shapes
Diagonals mislead when ratios differ. A 34-inch 21:9 ultrawide has the same height as a 27-inch 16:9 monitor and is only 33% wider, not 26% larger in every direction. A 27-inch 4:3 screen has more area (350 in²) than a 27-inch 16:9 screen (312 in²). Compare width and height, or area, rather than the diagonal when choosing between shapes.
Viewing distance
For television, a common guideline is a distance of 1.5 to 2.5 times the diagonal for HD and 1 to 1.5 times for 4K, where the finer pixels allow sitting closer. A 55-inch 4K TV suits a sofa 1.4 to 2.1 m away. For desktop monitors, the height matters most: the top of the screen should sit at or slightly below eye level, which favours screens under 14 inches tall for a seated user unless the desk is deep. The screen PPD calculator works out how sharp a screen looks from a given distance.
Common mistakes
- Measuring the bezel as screen. Diagonals refer to the active picture area only.
- Filling all three fields. Enter either the diagonal or the width and height, not both.
- Assuming the ratio. Many laptops are 16:10 or 3:2; check the specification.
- Forgetting units. The tool works in inches. Divide centimetres by 2.54 first, or use the length calculator.
Related tools
The pixel to inches converter relates resolution to physical size, and the area converter turns width × height into square centimetres or square feet. The file size converter and data rate converter cover the streaming side of a new screen.
External references
Frequently asked questions
How wide is a 65-inch TV?
About 56.7 inches (144 cm) for the panel at 16:9, plus bezels; most 65-inch sets are 57 to 58 inches wide overall.
Is a bigger diagonal always a bigger screen?
Not across different aspect ratios. A wider ratio spends more of the diagonal on width and less on height.
How do I convert the result to centimetres?
Multiply inches by 2.54. A 23.53-inch width is 59.8 cm.
Why is my measured diagonal slightly less than the advertised size?
Manufacturers round up to the nearest half inch or inch, and some quote the glass rather than the active area. A “27-inch” monitor is often 26.9 inches.
What aspect ratio should I enter for a phone?
Enter width and height from the specification instead, since phone ratios such as 19.5:9 or 20:9 are not in the preset list.