Screen dimensions, pixel density and viewing distance
A screen’s size is quoted as its diagonal, but what you usually need is its width and height — to see whether a TV fits a cabinet, whether two monitors sit side by side on a desk, or how much bigger a 65-inch television really is than a 55-inch one. This screen size calculator turns a diagonal and aspect ratio into width, height and area in inches and centimetres, and, given a resolution, the pixel density (PPI), pixel pitch and the “retina” distance beyond which you can no longer see pixels.
You can also work backwards from a measured width and height, and compare two screens drawn to the same scale. Presets cover common phones, laptops, monitors and TVs; any resolution and any aspect ratio (including custom ones) work.
It runs entirely in your browser. For print resolution and image sizes, use the DPI calculator; to see your own display’s resolution, open the screen resolution checker.
How to use the Screen Size Calculator
- Enter screen A’s Diagonal in inches or cm and its Resolution.
- Leave Aspect ratio on “From the resolution”, or pick a ratio such as 16:9, 21:9 or a custom one.
- Read the width and height, area, PPI, pixel pitch and the viewing distances.
- Switch to From width × height if you have measured the visible picture and want the diagonal.
- Fill in screen B under Compare with another screen to see both outlines to scale and the difference in area.
Screen Size Calculator features
Both directions
Diagonal + aspect ratio → width and height, or width and height → diagonal and ratio.
Pixel density
PPI and pixel pitch from the resolution, with megapixels; ratios such as 16:9 or 43:18 are recognised automatically.
Viewing distance
The 1-arcminute “retina” distance for 20/20 vision, plus THX (40°) and SMPTE (30°) seating distances for films.
Scaled comparison
Two screens drawn to the same scale, with a side-by-side table and the area difference in percent; outlines glide to their new size.
Inches and centimetres
Every length in both units, so it works for shopping in India, the UK or the US.
The formulas
For aspect ratio r = width ÷ height and diagonal d: width = d × r ÷ √(r² + 1) and height = d ÷ √(r² + 1). A 16:9 screen is therefore 0.872 of its diagonal wide and 0.490 tall — a 27-inch monitor is 23.5 × 13.2 inches (59.8 × 33.6 cm).
Pixel density is the pixel count along the diagonal divided by the diagonal: PPI = √(horizontal² + vertical²) ÷ d. 2560 × 1440 on 27 inches gives 108.8 PPI. The retina distance is where one pixel subtends one arcminute, the resolving limit of 20/20 vision: about 3438 ÷ PPI inches — 31.6 inches (80 cm) for that monitor.
Common sizes at 16:9
| Diagonal | Width × height (in) | Width × height (cm) | THX–SMPTE distance |
|---|---|---|---|
| 24″ | 20.9 × 11.8 | 53.1 × 29.9 | 0.7–1.0 m |
| 27″ | 23.5 × 13.2 | 59.8 × 33.6 | 0.8–1.1 m |
| 32″ | 27.9 × 15.7 | 70.8 × 39.8 | 1.0–1.3 m |
| 43″ | 37.5 × 21.1 | 95.2 × 53.5 | 1.3–1.8 m |
| 50″ | 43.6 × 24.5 | 110.7 × 62.3 | 1.5–2.1 m |
| 55″ | 47.9 × 27.0 | 121.8 × 68.5 | 1.7–2.3 m |
| 65″ | 56.7 × 31.9 | 143.9 × 80.9 | 2.0–2.7 m |
| 75″ | 65.4 × 36.8 | 166.0 × 93.4 | 2.3–3.1 m |
| 85″ | 74.1 × 41.7 | 188.2 × 105.8 | 2.6–3.5 m |
Tips
- Going from 16:9 to an ultrawide of the same diagonal makes the screen wider but noticeably shorter; compare heights before you buy.
- Doubling the diagonal quadruples the area: a 65″ TV has 40% more picture than a 55″.
- Allow for the stand and bezel: the outside of a TV is usually 1–3 cm larger than the picture in each direction.
- If your monitor feels blurry at a normal distance, its PPI is probably below about 90; text looks sharp from roughly 110 PPI at desk distance.
Screen Size Calculator FAQ
How do I calculate screen width and height from the diagonal?
Use the screen size calculator: enter the diagonal and the aspect ratio. Mathematically, width = d × r ÷ √(r² + 1) and height = d ÷ √(r² + 1), where r is the ratio of width to height.
How big is a 55-inch TV in cm?
A 55″ 16:9 TV has a picture about 121.8 × 68.5 cm (47.9 × 27.0 in); the diagonal is 139.7 cm.
What is a good PPI for a monitor?
At about 60 cm away, around 110 PPI looks sharp (27″ 1440p); 4K at 27″ gives 163 PPI for very crisp text at 150% scaling. Phones are usually 400 PPI or more because they are held close.
How far should I sit from my TV?
For a cinema-like view, THX recommends a 40° field of view and SMPTE at least 30° — about 1.2 to 1.6 times the diagonal for 16:9. The calculator shows both distances.
Is a 21:9 screen the same height as a 16:9 screen of the same size?
No — it is shorter. A 34″ 21:9 ultrawide is about the same height as a 27″ 16:9 monitor.
How do I find my screen’s resolution?
Open the screen resolution checker, then enter the numbers here. For pixels per inch in print, use the DPI calculator; for ratios on their own, the aspect ratio calculator.