What resolution actually counts
Resolution is simply the number of individual pixels a screen has, given as width by height: 1920×1080, for instance, is 1920 pixels across and 1080 down, just over two million pixels in total. It says nothing on its own about how large the screen is or how sharp it looks; a 1920×1080 image can be shown on a 5-inch phone or a 75-inch television, and it is the same 2,073,600 pixels either way, arranged very differently in physical space.
The common resolution names
| Name | Pixels | Common use |
|---|---|---|
| 720p / HD | 1280×720 | Budget displays, older broadcast |
| 1080p / Full HD | 1920×1080 | The most common monitor and TV resolution |
| 1440p / QHD | 2560×1440 | Mid-to-high monitors, some phones |
| 4K / UHD | 3840×2160 | Premium monitors, most new TVs |
| 8K | 7680×4320 | High-end TVs, limited native content |
Each step up roughly doubles both the horizontal and vertical pixel count, which quadruples the total: 4K has four times the pixels of 1080p, not twice, even though "4K" sounds like a factor of four on its own name rather than a description of the result.
Resolution, PPI and physical size are three different things
Confusion mostly comes from these three getting collapsed into one idea. Resolution is the pixel count. Physical size is the screen's diagonal measurement in inches. Pixel density, PPI, is what you get from combining the two: the same resolution can be sharp or soft entirely depending on the size of the panel it is drawn on. A 1080p resolution on a 24-inch monitor sits at roughly 92 PPI, comfortable for normal desk use; the same 1080p pixel count stretched across a 55-inch TV drops to around 40 PPI, noticeably softer up close, which is why televisions are designed to be watched from further away than monitors are.
Aspect ratio changes the shape, not just the count
Resolution numbers imply an aspect ratio, the ratio between width and height. 1920×1080 is 16:9, the standard widescreen shape for most monitors, laptops and TVs made in the last fifteen years. Ultrawide monitors commonly run 21:9, wider still, at resolutions like 3440×1440. Older 4:3 displays, closer to square, are largely gone from consumer screens but persist in some professional and broadcast equipment. Two screens can share a resolution's pixel count while looking like a completely different shape, so resolution alone does not fully describe a screen either.
Why your browser might disagree with the spec sheet
Operating systems apply display scaling, most often on high-density laptop and phone screens, to keep text and interface elements a readable size rather than shrinking them in proportion to the extra pixels. A native 3840×2160 panel set to 150% scaling reports roughly 2560×1440 to most applications, including a web browser, even though the physical panel has not changed. This is the same mechanism behind why on-screen rulers drawn from resolution alone are unreliable: the number a page can read is not always the number printed on the box.
The Screen Size Checker shows exactly what your browser is currently reporting: resolution, pixel density and aspect ratio together, alongside a calibrated measurement of the screen's actual physical size for comparison.