How we calculate
Every number on MonitorScale is calculated from two inputs: the panel’s diagonal size and its resolution. Nothing is estimated from photos or marketing images. Square pixels are assumed, which holds for all modern displays.
Physical size
Width = diagonal × w ÷ √(w² + h²), and height = diagonal × h ÷ √(w² + h²), where w and h are the resolution in pixels. A 27″ 2560 × 1440 panel is therefore 23.53″ × 13.24″ (59.8 × 33.6 cm). These are the visible screen dimensions. Bezels and stands add a model-specific amount.
Pixel density (PPI)
PPI = √(w² + h²) ÷ diagonal. Pixel pitch is 25.4 ÷ PPI millimetres.
Viewing distances
- Pixels vanish beyond: the distance at which one pixel spans one arcminute, the resolving limit of 20/20 vision: 1 ÷ (PPI × tan(1/60°)).
- Comfortable distance: the distance at which the screen height spans about 22° of vision, which keeps the whole screen in a relaxed field of view. Using height keeps the result sensible for ultrawides.
The Mac sharpness verdict
macOS renders apps at 1× or 2× and sizes its interface for about 110 points per inch on desktop displays. Other interface sizes are produced by rendering a 2× image and resampling it to the panel, which slightly softens text. We classify displays by PPI:
| PPI | Verdict | What it means |
|---|---|---|
| Below 95 | Visible pixels | 1× rendering with noticeably pixelated text. |
| 95–125 | Sharp, not Retina | Clean 1× rendering at a comfortable UI size. |
| 125–140 | Scaled, mostly fine | Best used in a scaled mode; mild softness most people accept. |
| 140–176 | Scaling compromise | Too dense for 1×, not dense enough for comfortable 2×. |
| 176 and above | Retina sharp | Pixel-exact 2× rendering. |
The recommended “looks like” resolution is the macOS scaled mode whose point density lands closest to110 points per inch. Band edges are judgement calls informed by Apple’s own display choices and widely shared user experience; individual sensitivity to softness varies. Built-in Windows laptop screens get no Mac verdict.
The pixel loupe
The loupe draws the same physical patch of each screen on its real pixel grid. Text is set at 13 pt and icons at 20 pt and 12 pt, at each display’s recommended UI scale; the image fills the same physical area on both screens. Everything is drawn as vectors, so each display renders it at its own true resolution. For resampled Mac modes the loupe renders into a larger 2× buffer and scales it down with high-quality smoothing, approximating what macOS does.
The subpixel view splits each pixel into red, green and blue stripes, the layout of most LCD monitors. Text is magnified a further 2× and drawn with pure stripes. For the image and icons each stripe keeps part of its pixel’s colour so the picture stays recognisable. OLED panels use other layouts, so treat this view as an illustration. The loupe is a simulation for comparison, not a photograph of a specific panel.
True size
Browsers report CSS pixels, not physical size, so the scene is always correct relative to itself but not in absolute size. True size mode uses a one-time calibration against an ID-1 card (85.60 × 53.98 mm) to convert CSS pixels to millimetres on your screen.
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