Screen Size Calculator
Enter your screen diagonal and resolution to get the physical width, height, and area, plus pixel density in PPI, dot pitch, total megapixels, aspect ratio, and the optimal viewing distance. Works for TVs, monitors, laptops, tablets, and projector screens. Switch between inches and centimetres at any time.
How to use this calculator
Enter the diagonal size of your screen (as printed on the box or listed in specs), choose the aspect ratio from the preset list, and optionally enter the resolution (pixel width and height). The calculator returns the physical width, height, and area of the display, plus pixel density (PPI), dot pitch, total megapixels, and optimal viewing distance. Switch between inches and centimetres using the units selector at the top - all results update instantly.
How screen dimensions are calculated
Screen manufacturers report diagonal size, not width or height, because a single number describes screens of any shape. To find width and height from the diagonal, the calculator uses the aspect ratio and the Pythagorean theorem. If the aspect ratio is W:H, the height equals the diagonal divided by the square root of (W/H)^2 + 1, and the width is the height multiplied by W/H. For a 27-inch 16:9 screen, that gives a height of about 13.25 inches and a width of about 23.54 inches.
What is pixel density (PPI)?
Pixel density, measured in pixels per inch (PPI), tells you how tightly packed the pixels are across the screen surface. Higher PPI means sharper images and text. It is calculated as the diagonal pixel count (from the Pythagorean theorem applied to the resolution) divided by the diagonal size in inches. A 27-inch QHD monitor (2560x1440) has about 109 PPI, which is comfortable at arm's length. A modern smartphone at 460 PPI appears perfectly sharp because individual pixels are far too small for the eye to resolve. Dot pitch is the inverse - the physical size of one pixel in millimetres. A smaller dot pitch means a sharper, denser display.
Optimal viewing distance
The ideal viewing distance balances comfort and immersion. The 30-degree field-of-view rule, widely used by home cinema enthusiasts and ergonomists, sets the ideal distance so the screen spans roughly 30 degrees of your horizontal vision. This equals (screen width / 2) divided by the tangent of 15 degrees. For a 27-inch 16:9 monitor, that works out to about 36 inches (91 cm) - roughly arm's length for most people. The minimum viewing distance is the point at which pixels become visible, calculated from the dot pitch and the 1-arc-minute limit of the human eye. For TVs in living rooms, the 30-degree rule often results in distances from 6 to 12 feet depending on screen size.
Common screen sizes and PPI reference
| Device type | Typical diagonal | Common resolution | Typical PPI | Sharpness |
|---|---|---|---|---|
| Smartphone | 6 in | 2532 x 1170 (FHD+) | 460 | Retina / very high |
| Tablet | 11 in | 2388 x 1668 | 264 | High |
| Laptop (FHD) | 15.6 in | 1920 x 1080 | 141 | Good |
| Laptop (4K) | 14 in | 3840 x 2160 | 314 | Very high |
| Desktop monitor | 27 in | 2560 x 1440 (QHD) | 109 | Good |
| Desktop monitor 4K | 27 in | 3840 x 2160 | 163 | High |
| Gaming ultrawide | 34 in | 3440 x 1440 | 109 | Good |
| TV (FHD) | 55 in | 1920 x 1080 | 40 | Low - view from distance |
| TV (4K) | 55 in | 3840 x 2160 | 80 | Acceptable from sofa |
| TV (4K) | 65 in | 3840 x 2160 | 68 | OK from 8+ ft |
| Cinema projector | 150 in | 3840 x 2160 | 29 | Low - far viewing |
Typical PPI values for popular device categories at common resolutions.
Frequently asked questions
Does screen diagonal include the bezel?
No. Manufacturers measure and advertise the diagonal of the active display area - the part that lights up - not the outer plastic or metal frame (bezel). When measuring your own screen, measure corner to corner of the visible image area only, not the physical chassis.
What is a good PPI for a monitor?
For a desktop monitor viewed at arm's length (around 24-30 inches), a PPI of 90-110 is considered good; 140-160 is very sharp; above 200 is effectively retina quality where pixels are indistinguishable at normal distances. For a TV watched from 8-10 feet, 40-80 PPI is perfectly acceptable because pixels look much smaller from far away.
How do I find my screen aspect ratio?
Check the display specifications in your device settings or on the manufacturer's website. Common aspect ratios are 16:9 (most TVs and monitors), 16:10 (many business laptops), 4:3 (older monitors and some tablets), and 21:9 (ultrawide gaming and productivity monitors). If you know the resolution, divide width pixels by height pixels: 1920/1080 = 1.78, which matches 16:9 (16/9 = 1.78). This calculator also shows the simplified ratio when you enter resolution.
What is the right TV size for my room?
The 30-degree field-of-view guideline gives a comfortable, cinematic feel. At 8 feet (about 243 cm) from the sofa, a 55-65 inch screen fits well. At 10 feet (305 cm), a 65-75 inch screen is comfortable. The 4K sharpness threshold sits at roughly 1.5x the screen height for a 4K TV, which in practice means getting closer than you would with a 1080p set of the same size.
Why do two monitors with the same resolution look different in sharpness?
Because sharpness depends on pixel density, not raw resolution. A 1920x1080 panel on a 24-inch monitor has about 92 PPI and looks sharp at arm's length, but the same resolution on a 32-inch panel drops to about 69 PPI, which can look noticeably less crisp. Always compare PPI, not just resolution, when evaluating display sharpness.