Why use this calculator
PPI on its own is a misleading specification, because it describes the panel and says nothing about the eye looking at it. A phone at 460 PPI held 14 inches away and a television at 80 PPI viewed from 100 inches deliver almost identical apparent sharpness, and a huge cinema screen at under 10 PPI looks perfectly sharp from the back row.
What matters is the angle each pixel subtends at your eye, measured as pixels per degree, and normal 20/20 vision runs out at about 60 of them. This calculator gives you PPI for comparing panels, pixels per degree for your actual desk or sofa, and the distance at which any given panel becomes indistinguishable from a perfect one, which is the number that decides whether a resolution upgrade is worth paying for.
How to use it
- Enter the native resolution of the display, which is the figure on the specification sheet rather than whatever the operating system is currently set to, because running a panel off its native resolution introduces its own softness.
- Enter the diagonal size in inches as advertised, measured corner to corner across the visible panel rather than the bezel.
- Then enter how far your eyes actually sit from the screen: roughly 20 to 28 inches at a desk, 12 to 16 inches for a phone, 16 to 20 inches for a laptop on your lap, and 80 to 120 inches for a television in a living room.
- Measure it once with a tape rather than estimating, because this input moves the answer more than any of the others.
What each result means
- PPI (pixels per inch)
- The panel's own pixel density. Use it to compare two displays like for like, not to judge how sharp one will look.
- Pixels per degree
- How many pixels fall within one degree of your field of view at your stated distance. Sixty or more and the eye cannot resolve individual pixels.
- Sharpness at this distance
- A plain reading of the pixels-per-degree figure, from pixels clearly visible up to fully retina at your seating position.
- To look retina at this distance
- The pixel density, and the matching resolution at the same shape, that a screen of this size would need to reach 60 pixels per degree where you sit. Use it to judge whether an upgrade is worth buying.
- Pixel density class
- Where the raw PPI sits among typical devices, from a standard desktop panel to phone-class density.
- Distance where pixels disappear
- Move back at least this far and individual pixels become unresolvable, so extra resolution buys nothing more.
- Dot pitch (mm)
- The physical spacing between pixel centres. Smaller means denser, and it is the specification monitors quoted before PPI took over.
- Panel size
- The actual width and height of the viewable area, which is what you need when checking a monitor will fit a desk or a mount.
- Megapixels
- Total pixels in millions, which drives the load on a graphics card and the bandwidth a cable has to carry.
The formula
PPI = the square root of (width in pixels squared plus height in pixels squared), divided by the diagonal size in inches
Dot pitch in millimetres = 25.4 divided by PPI
Pixels per degree = PPI times viewing distance in inches times the tangent of one degree, which is 0.017455
The distance at which pixels vanish = the size of one pixel in inches, which is 1 divided by PPI, divided by the tangent of one arcminute, which is 0.00029089, since one arcminute is the accepted resolution limit of 20/20 vision
How this number is used in practice
The practical question is almost always whether a higher resolution is worth the money at the distance you will actually use it. A 27-inch 1440p monitor at desk distance lands near 46 pixels per degree, which is short of the 60 where the eye gives up, so text edges are still faintly visible and a 4K panel of the same size is a genuine improvement.
A 65-inch 4K television viewed from eight feet is already past 60 pixels per degree, which is why 8K makes almost no visible difference in a normal living room and why cinema chains care far more about brightness and contrast than about pixel count.
Operating system scaling complicates the picture and is worth understanding before buying. The web and most interfaces are laid out in reference pixels defined against roughly 96 dots per inch at arm's length, so on a high-density panel the system draws each interface pixel using several physical ones.
That is what makes text look smooth, but it means a 4K 27-inch monitor at 150 per cent scaling shows the same amount of content as a 1440p panel while rendering it more finely. If you want more workspace rather than sharper text, a larger panel at moderate density beats a small very dense one.
Distance also explains the outdoor case that looks absurd on paper. Stadium and billboard displays run at densities of a few pixels per inch, which would be unusable on a desk, yet appear perfectly sharp because nobody stands closer than tens of metres. The same reasoning applies in reverse to a phone: held at 14 inches, it needs several times the density of a desktop monitor just to match it, which is why phone panels have led the pixel-density race for years.
Worked examples
A 27-inch 2560 by 1440 desktop monitor at 24 inches
108.8 PPI and 45.6 pixels per degree, rated excellent but short of the retina threshold of 60.
A 27-inch 4K panel at the same desk distance
163.2 PPI and 68.4 pixels per degree, which clears 60 and is genuinely retina at that seating position.
A 6.1-inch phone at 2532 by 1170 held 14 inches away
About 457.3 PPI and 111.7 pixels per degree, far beyond what the eye can resolve.
A 65-inch 4K television viewed from 96 inches
Only 67.8 PPI, yet 113.6 pixels per degree, which is why 4K already exceeds what a living room can show.
When people use it
- Deciding whether a 4K monitor is worth it over 1440p at your desk distance
- Checking whether an 8K television would be visible at all from your sofa
- Comparing two laptops or phones on real sharpness rather than marketing numbers
- Choosing a display for photo editing or typography where fine detail matters
- Working out how far back to sit from a projector or a large television
Tips
- Compare displays on pixels per degree at your real distance, not on PPI. PPI describes the panel; only the angle describes what you see.
- Sixty pixels per degree is the accepted limit of 20/20 vision. Beyond it, extra resolution costs money and graphics performance for no visible gain.
- Measure your viewing distance once with a tape. Most people sit further from a monitor than they estimate and closer to a television.
- Always drive a panel at its native resolution. A non-native mode interpolates and looks softer than the pixel density suggests.
- On a high-density panel, use system scaling rather than a lower resolution when text is too small; scaling keeps the sharpness.
- Contrast, brightness, colour accuracy and refresh rate usually affect perceived quality more than pixel density once you are past about 45 pixels per degree.
What it assumes, and where it stops being accurate
- Pixels are square and evenly spaced, which holds for standard RGB stripe panels but not for some OLED subpixel layouts.
- The retina threshold uses one arcminute of visual acuity, the standard definition of 20/20 vision. Sharper eyesight resolves finer detail.
- The diagonal is the viewable panel measurement, not including the bezel, and matches the resolution entered.
- Viewing distance is constant, whereas in practice people lean in and move back, especially when reading fine text.
- Subpixel rendering, anti-aliasing and display scaling all change perceived sharpness and are not modelled here.
- Pixels per degree uses a flat-panel approximation, so it is slightly optimistic at the far edges of a very large or curved screen.
Terms used on this page
- PPI
- Pixels per inch, the count of pixels along one inch of the panel surface.
- Pixels per degree
- Pixels falling within one degree of the viewer's field of view, the measure that accounts for distance.
- Dot pitch
- The physical spacing in millimetres between the centres of adjacent pixels.
- Visual acuity
- The eye's resolving power. 20/20 vision distinguishes detail about one arcminute apart.
- Reference pixel
- The CSS unit defined as an angle at arm's length rather than a fixed dot, which is why interfaces scale on dense panels.
Questions people ask
- What PPI counts as a good screen?
- It depends entirely on distance. Around 110 PPI is normal for a desktop monitor, 160 or more is considered high for one, and phones sit above 400 because they are held so close. A television at 70 PPI can look flawless from across a room, so judge by pixels per degree instead.
- What are pixels per degree and why do they matter?
- It is how many pixels fall inside one degree of your field of view, which combines pixel density with how far away you sit. Normal 20/20 vision resolves about 60 per degree, so once a display passes that at your seating position, extra pixels cannot be seen at all.
- Is 8K worth it for a living room television?
- Very rarely. A 65-inch 4K television at eight feet already delivers well over 60 pixels per degree, so the eye cannot resolve its pixels. Reaching a visible benefit from 8K would mean sitting roughly half as far away or buying a much larger screen. Brightness, contrast and colour matter far more.
- What is dot pitch?
- The physical distance in millimetres between the centres of neighbouring pixels, and the inverse of pixel density. A 0.23 mm dot pitch is about 110 PPI. It was the standard sharpness specification in the CRT era and still appears on industrial and professional display datasheets.
- Why does my high-PPI screen show less content, not more?
- Because the operating system is scaling the interface. A 4K 27-inch monitor at 200 per cent scaling shows exactly the content of a 1080p panel, drawn with four times the pixels. That is a sharpness upgrade rather than a workspace upgrade; for more workspace, lower the scaling or choose a larger panel.
- Does higher PPI always look better?
- Only up to the point where your eye stops resolving the difference, which this calculator reports as the distance where pixels disappear. Past that, higher density costs graphics performance and battery life for nothing visible. Panel brightness, contrast ratio and colour accuracy keep improving the picture long after density stops mattering.
Use this with
Screen PPI Calculator answers one part of the question. These pick up where it stops: Aspect Ratio Calculator, Data Storage Converter, Length Converter and Area Calculator.
Where these figures come from
This calculation is jurisdiction-neutral arithmetic. No country-specific rules are applied.
- W3C: CSS Values and Units, reference pixel. Defines the CSS reference pixel as an angle subtended at arm's length, not a fixed dot
- VESA: Video Electronics Standards Association. Display resolution, timing and DisplayHDR standards
- ITU-R: Recommendation BT.709. The recommendation that fixed 16:9 as the HDTV picture aspect ratio
Screen PPI Calculator produces an estimate for general information. It is not financial, tax, medical, legal or engineering advice. read the full disclaimer. Spotted a wrong number? Report it and it gets fixed. The form picks up this calculator and the inputs you used.