Screen Resolution Calculator
Screen resolution is the number of pixels across the width and height of a display. Combined with the physical screen size, it determines pixel density (PPI), sharpness, and display quality. This screen resolution calculator takes three inputs: horizontal pixel count, vertical pixel count, and the diagonal screen size in inches. It then calculates total megapixels (width x height / 1,000,000), pixels per inch (PPI) using the Pythagorean theorem, the simplified aspect ratio, and the display class (HD, Full HD, QHD, or 4K). Use this tool to compare monitors before buying, verify a display spec, or understand why two screens with the same resolution look different depending on size.
Display class reference
| Class | Resolution | Megapixels | Common name |
|---|---|---|---|
| HD | 1280 x 720 | 0.92 MP | 720p |
| Full HD (FHD) | 1920 x 1080 | 2.07 MP | 1080p |
| QHD / 2K | 2560 x 1440 | 3.69 MP | 1440p |
| 4K UHD | 3840 x 2160 | 8.29 MP | 2160p |
| 8K UHD | 7680 x 4320 | 33.18 MP | 4320p |
Formula
Megapixels = (width x height) / 1,000,000
PPI = sqrt(width squared + height squared) / diagonal inches
Dot pitch (mm) = 25.4 / PPI
Screen resolution: frequently asked questions
What is PPI (pixels per inch)?
PPI (pixels per inch) is the pixel density of a display, measuring how many pixels fit into one inch of screen. It is calculated as: PPI = square root of (width squared plus height squared) divided by the diagonal screen size in inches. Higher PPI means sharper, more detailed images. Apple's Retina displays are generally above 220 PPI. Smartphone displays typically range from 300 to 460 PPI.
What is the difference between HD, FHD, QHD, and 4K?
HD (High Definition) is 1280x720 pixels (720p). Full HD (FHD) is 1920x1080 pixels (1080p). QHD (Quad HD) is 2560x1440 pixels (1440p), four times the pixel count of 720p. 4K UHD (Ultra High Definition) is 3840x2160 pixels, four times the pixel count of 1080p. 8K UHD is 7680x4320 pixels. The 'K' in 4K refers to approximately 4,000 horizontal pixels.
What is a good PPI for a monitor?
For desktop monitors viewed from 50-70 cm: 90-110 PPI is standard for a 27-inch 1440p monitor. 110-140 PPI is good (a 27-inch 4K monitor is about 163 PPI). For laptops at typical arm's length: 150-220 PPI is the norm for 13-16 inch screens. For smartphones held at 30-40 cm: 300-460 PPI is typical and desirable. Below 90 PPI on a desktop monitor, individual pixels may be visible.
How do I calculate total megapixels?
Total megapixels = (horizontal pixels x vertical pixels) / 1,000,000. For example, a 4K display (3840x2160) has 3840 x 2160 = 8,294,400 pixels, which is approximately 8.29 megapixels. A 1080p display (1920x1080) has 2,073,600 pixels, approximately 2.07 megapixels.
What aspect ratio is 16:9?
16:9 (sixteen to nine) is the standard widescreen aspect ratio used for most modern monitors, televisions, laptops, and smartphones in landscape mode. It replaced the older 4:3 ratio (used in old televisions and early computer monitors). Cinematic displays may use 21:9 (ultrawide) or 32:9 (super ultrawide). Vertical smartphone screens are effectively 9:16 in portrait orientation.
Official sources
- Consumer Technology Association (CTA): 4K Ultra HD standard definitions.
- VESA DisplayHDR: VESA display performance standards.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.