Screen PPI and viewing distance calculator
Compare monitors and TVs by how sharp they actually look. Enter the resolution and diagonal size to get pixel density, physical dimensions and the viewing distance at which individual pixels become invisible.
By Zubair Abid. Updated .
Quick answer
PPI = √(width² + height²) ÷ diagonal in inches. A 27-inch 1440p monitor (2560 × 1440) has about 109 PPI; a 27-inch 4K monitor about 163 PPI. With 20/20 vision, pixels stop being visible beyond roughly 3,438 ÷ PPI inches: about 32 inches for 109 PPI.
The screen
How is PPI calculated?
PPI = √(Width px² + Height px²) ÷ Diagonal (in)
The top part is the number of pixels along the diagonal, found with Pythagoras. Dividing by the diagonal length in inches gives pixels per inch. Higher PPI means smaller pixels and sharper text at the same distance.
Distance where pixels blend (in) ≈ 3,438 ÷ PPIBased on 20/20 vision resolving about 1 arcminute.
Common screens compared
| Screen | Resolution | PPI | Pixels blend beyond |
|---|---|---|---|
| 24-inch monitor | 1920 × 1080 | 92 | About 37 in (94 cm) |
| 27-inch monitor | 2560 × 1440 | 109 | About 32 in (80 cm) |
| 27-inch monitor | 3840 × 2160 | 163 | About 21 in (54 cm) |
| 34-inch ultrawide | 3440 × 1440 | 110 | About 31 in (79 cm) |
| 55-inch TV | 3840 × 2160 | 80 | About 43 in (109 cm) |
| 6.1-inch phone | 1170 × 2532 | 457 | About 7.5 in (19 cm) |
This explains why a 55-inch 4K TV looks sharp from the sofa despite low PPI, and why 1080p on a 27-inch monitor looks soft at a desk: you sit closer than the distance where its pixels blend.
What PPI should you look for?
- Desk monitors (50 to 70 cm away): 100 to 110 PPI is comfortable; 140+ looks crisp for text and photo work, often with display scaling.
- Laptops: 150 to 220 PPI is typical at 13 to 16 inches.
- TVs: Pick size by viewing distance rather than PPI. At 2.5 m, 4K on a 55 to 65-inch screen is past the point where pixels are visible.
- Gaming: Higher PPI costs frame rate. 27-inch 1440p is a popular balance of sharpness and GPU load.
PPI isn't everything: panel type, brightness, scaling and viewing distance all change how sharp a screen looks. Use PPI to compare screens of different sizes on equal terms.
How big is the screen really?
Two screens with the same diagonal can have very different widths. A 34-inch 21:9 ultrawide is about as tall as a 27-inch 16:9 monitor but much wider. The calculator gives width and height so you can check desk space or a wall mount before buying.
Dot pitch (the distance between pixel centres, in millimetres) is just the inverse of PPI: 25.4 ÷ PPI. Smaller dot pitch = sharper image.