Unit & Measurement Tables
Screen Resolution Table
A resolution is two numbers, but almost every question about a screen needs a third: how big is it? The same 1920 × 1080 panel is a sharp laptop screen at 13 inches and a coarse desktop monitor at 27 inches, because pixel density depends on the diagonal, not on the count.
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Pixel density is pure geometry. The diagonal in pixels comes from the Pythagorean theorem applied to the width and height, and dividing that by the diagonal in inches gives pixels per inch. There is nothing to look up: a 27 inch 2560 × 1440 panel has 3,686 pixels on its diagonal and therefore 108.8 ppi, which is why it looks similar to a 24 inch 1080p screen at 91.8 ppi despite having nearly twice the pixels.
The naming is the confusing part. 4K refers to roughly 4,000 horizontal pixels, but consumer 4K is 3,840 × 2,160 while cinema DCI 4K is 4,096 × 2,160 — a different aspect ratio entirely. 1440p is also called QHD, and 2560 × 1440 is neither twice 1080p in each direction nor exactly 16:9 after rounding, though it is close enough that the label sticks.
The tables below give the counts, the ratios in lowest terms and a density grid across common diagonals. The last table pairs real panel sizes with the viewing distance at which individual pixels stop being resolvable, which is the number that actually determines whether a higher resolution is worth paying for.
Common resolutions: pixels, megapixels and aspect ratio
| Name | Width | Height | Total pixels | Megapixels | Aspect ratio |
|---|---|---|---|---|---|
| 720p (HD) | 1,280 | 720 | 921,600 | 0.92 | 16:9 |
| 1080p (Full HD) | 1,920 | 1,080 | 2,073,600 | 2.07 | 16:9 |
| 1440p (QHD) | 2,560 | 1,440 | 3,686,400 | 3.69 | 16:9 |
| 4K UHD | 3,840 | 2,160 | 8,294,400 | 8.29 | 16:9 |
| 5K | 5,120 | 2,880 | 14,745,600 | 14.75 | 16:9 |
| 8K UHD | 7,680 | 4,320 | 33,177,600 | 33.18 | 16:9 |
| WUXGA | 1,920 | 1,200 | 2,304,000 | 2.30 | 8:5 |
| UWQHD (34 inch) | 3,440 | 1,440 | 4,953,600 | 4.95 | 43:18 |
| XGA | 1,024 | 768 | 786,432 | 0.79 | 4:3 |
| SVGA | 800 | 600 | 480,000 | 0.48 | 4:3 |
4K is 3,840 × 2,160 because consumer 4K is UHD, not the cinema DCI 4K standard of 4,096 × 2,160. The name refers to the horizontal count rounded to the nearest thousand.
Pixel density by resolution and diagonal
| Resolution | 13.3 in | 15.6 in | 24 in | 27 in | 32 in | 34 in | 43 in | 55 in | 65 in |
|---|---|---|---|---|---|---|---|---|---|
| 720p (HD) | 110.4 | 94.1 | 61.2 | 54.4 | 45.9 | 43.2 | 34.2 | 26.7 | 22.6 |
| 1080p (Full HD) | 165.6 | 141.2 | 91.8 | 81.6 | 68.8 | 64.8 | 51.2 | 40.1 | 33.9 |
| 1440p (QHD) | 220.8 | 188.3 | 122.4 | 108.8 | 91.8 | 86.4 | 68.3 | 53.4 | 45.2 |
| 4K UHD | 331.3 | 282.4 | 183.6 | 163.2 | 137.7 | 129.6 | 102.5 | 80.1 | 67.8 |
| 5K | 441.7 | 376.6 | 244.8 | 217.6 | 183.6 | 172.8 | 136.6 | 106.8 | 90.4 |
| 8K UHD | 662.5 | 564.8 | 367.2 | 326.4 | 275.4 | 259.2 | 204.9 | 160.2 | 135.6 |
Pixels per inch is the diagonal in pixels divided by the diagonal in inches. The same 1080p panel gives 92 ppi at 24 inches and 166 ppi at 13.3 inches.
Real panels with their density
| Panel | Resolution | Megapixels | Pixels per inch | Viewing distance |
|---|---|---|---|---|
| Laptop, 13.3 inch | 1,920 × 1,080 | 2.07 | 165.6 | 16 to 20 in |
| Laptop, 15.6 inch | 1,920 × 1,080 | 2.07 | 141.2 | 19 to 23 in |
| Desktop, 24 inch | 1,920 × 1,080 | 2.07 | 91.8 | 29 to 36 in |
| Desktop, 27 inch | 2,560 × 1,440 | 3.69 | 108.8 | 32 to 41 in |
| Desktop, 27 inch 4K | 3,840 × 2,160 | 8.29 | 163.2 | 32 to 41 in |
| Desktop, 32 inch 4K | 3,840 × 2,160 | 8.29 | 137.7 | 38 to 48 in |
| Ultrawide, 34 inch | 3,440 × 1,440 | 4.95 | 109.7 | 41 to 51 in |
| TV, 55 inch 4K | 3,840 × 2,160 | 8.29 | 80.1 | 66 to 83 in |
| TV, 65 inch 4K | 3,840 × 2,160 | 8.29 | 67.8 | 78 to 98 in |
Viewing distance follows the THX guidance of a 40 degree field of view, which works out to roughly 1.2 to 1.5 times the diagonal. Sitting closer than that is where individual pixels start to be visible.
How to Use These Tables
- Checking density: divide the diagonal in pixels by the diagonal in inches. 3840 × 2160 on a 32 inch panel is 137.7 ppi.
- Comparing monitors: a 27 inch 1440p screen is 108.8 ppi, close to a 24 inch 1080p at 91.8 ppi. The upgrade buys screen area more than sharpness.
- Estimating file size: a 4K frame is 8.29 megapixels, so an uncompressed 24-bit image is about 25 MB before any compression.
- Choosing a TV distance: multiply the diagonal by 1.2 to 1.5. A 55 inch 4K set wants 66 to 83 inches of viewing distance.
- Aspect ratio from pixels: divide width by height and reduce. 3440 / 1440 reduces to 43:18, which is the 21:9 class ultrawide.
Common Questions
Is 4K really 4,000 pixels wide?
Consumer 4K is 3,840 pixels wide, rounded up to the nearest thousand for marketing. Cinema DCI 4K is 4,096 × 2,160 and has a different aspect ratio, so the two are not interchangeable.
How do I calculate pixels per inch?
Take the square root of width squared plus height squared, then divide by the diagonal in inches. For 1920 × 1080 on 24 inches that is 2,202.9 / 24 = 91.8 ppi.
Is 1440p 16:9?
2560 × 1440 reduces to 16:9 exactly. It is called QHD and sits between 1080p and 4K, with 3.69 megapixels against 2.07 and 8.29.
Does a higher resolution always look sharper?
Only up to the point where your eye can resolve the pixels at your viewing distance. Beyond about 60 pixels per degree, which is roughly 100 ppi at arm's length, the gain is marginal.
What is the aspect ratio of an ultrawide monitor?
3440 × 1440 is 43:18, usually marketed as 21:9. True 21:9 would be 3360 × 1440, so the common panels are slightly wider than the label.
How many megapixels is 8K?
33.18 megapixels at 7680 × 4320, which is four times the 8.29 megapixels of 4K. File sizes scale the same way before compression.
More Unit & Measurement Tables
Sources
- ITU-R BT.2020 — parameter values for UHD television systems — International Telecommunication Union
- SMPTE ST 2036-1 — ultra high definition television, image parameter values — Society of Motion Picture and Television Engineers
- W3C — CSS Images Module, resolution units and pixel density — World Wide Web Consortium
Filed with Unit Conversion calculations.