How screen sizes are measured: TVs, monitors and phones
A screen’s size is the length of its diagonal, measured from one corner of the visible picture to the opposite corner. It doesn’t include the frame (bezel) around it. That’s why a “55-inch” TV is much less than 55 inches wide, and why two TVs with the same size can have different overall dimensions.
How to measure your screen
- Measure from the bottom-left corner of the picture area to the top-right corner. Don’t include the bezel.
- Use a tape measure, and measure in inches if you want to compare with how screens are sold.
- Round to the nearest whole inch. Manufacturers often round, so a “55-inch” TV may measure 54.6 inches.
Phones and laptops are measured the same way. On phones with rounded corners, the diagonal is measured as if the corners were square.
Width and height from the diagonal
Almost every TV and most monitors are 16:9. For that shape:
- width = diagonal × 0.872
- height = diagonal × 0.490
| Screen size | Width | Height |
|---|---|---|
| 24 in | 20.9 in (53.1 cm) | 11.8 in (29.9 cm) |
| 27 in | 23.5 in (59.8 cm) | 13.2 in (33.6 cm) |
| 32 in | 27.9 in (70.8 cm) | 15.7 in (39.8 cm) |
| 43 in | 37.5 in (95.2 cm) | 21.1 in (53.5 cm) |
| 50 in | 43.6 in (110.7 cm) | 24.5 in (62.3 cm) |
| 55 in | 47.9 in (121.8 cm) | 27.0 in (68.5 cm) |
| 65 in | 56.7 in (143.9 cm) | 31.9 in (80.9 cm) |
| 75 in | 65.4 in (166.0 cm) | 36.8 in (93.4 cm) |
These are the size of the picture only. Add the bezel and stand when checking whether a TV fits a space, usually 1–3 cm on each side for a modern TV.
Why the shape matters
Two screens with the same diagonal can have different areas. An ultra-wide 34-inch monitor (21:9) is wider but shorter than a 34-inch 16:9 screen would be. Compare screens of different shapes by width and height, not by their diagonal.
How big should a TV be?
A common rule of thumb for 4K TVs is to sit about 1 to 1.5 times the diagonal away. For a 55-inch TV that’s roughly 1.4 to 2.1 meters (4.5 to 7 feet). Sitting further back is fine; you just stop seeing all the detail a 4K picture has.
Screen size and on-screen rulers
The diagonal alone doesn’t tell your browser how big your screen is in real units, which is why an online ruler needs calibrating before it’s accurate.