Monitor PPI Calculator
Calculate the pixel density (PPI) of any monitor from its resolution and diagonal size.
How to use this tool
- Enter horizontal resolution, vertical resolution and screen diagonal in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your pixel density and the full breakdown beneath it.
Enter your screen resolution and diagonal size to calculate pixel density (PPI).
Formula
Diagonal pixels = √(horizontal² + vertical²)
PPI = Diagonal pixels / Screen diagonal (inches)
e.g. for 1920 × 1080 at 24 in: √(1920² + 1080²) = √(3 686 400 + 1 166 400) = √4 852 800 ≈ 2202.9 px; PPI = 2202.9 / 24 ≈ 91.79
How it works
Pixel density (PPI, pixels per inch) is calculated by finding the total number of pixels along the screen diagonal using the Pythagorean theorem, then dividing by the physical diagonal size in inches. The result is labelled by quality tier: below 90 PPI is considered low density, 90–139 is Standard HD, 140–219 is High DPI, and 220+ is Retina or Very High. A common mistake is comparing PPI across monitors of very different sizes without considering typical viewing distance: a 27-inch monitor at 109 PPI used at arm's length looks noticeably sharper than the raw number suggests when compared to a 55-inch TV at a similar PPI viewed from several feet away.
Worked example
Calculating PPI for a 1920×1080 monitor on a 24-inch screen
- Horizontal resolution = 1920 px, vertical resolution = 1080 px, diagonal = 24 in.
- Diagonal in pixels: √(1920² + 1080²) = √(3 686 400 + 1 166 400) = √4 852 800 ≈ 2202.9 px.
- PPI = 2202.9 / 24 ≈ 91.79.
- Quality label: 91.79 falls in the 90–139 range → Standard HD.
Pixel Density: 91.79 PPI | Quality Label: Standard HD
Common mistakes to avoid
- Using the screen marketed diagonal (e.g. 27 inches) which may include a bezel; actual viewable area diagonal is typically 0.1-0.5 inches smaller, slightly overstating the true PPI.
- Entering monitor dimensions in centimetres instead of inches -- the PPI formula requires screen size in inches; entering centimetres without converting (divide by 2.54) gives a PPI value about 2.5x too high.
- Confusing native resolution with output resolution -- if a 4K monitor is set to 1080p in display settings, the effective PPI for content rendering is that of the lower resolution, not the panel native PPI.
Key terms
- PPI (pixels per inch)
- A measure of pixel density — the number of individual pixels packed into one linear inch of screen; higher PPI produces sharper images at a given viewing distance.
- Retina display
- Apple's marketing term for a screen whose PPI is high enough that individual pixels are not discernible at a typical viewing distance; the threshold is roughly 220 PPI for a device held at arm's length.
- Native resolution
- The exact pixel grid a monitor is designed for (e.g. 1920 × 1080 or 2560 × 1440); running a monitor below its native resolution reduces sharpness because pixels must be scaled.
- High DPI (HiDPI)
- A general term for displays with pixel densities above roughly 140 PPI, where individual pixels become difficult to distinguish and text and icons appear noticeably crisp.
Frequently asked questions
- What is a good PPI for a monitor?
- 90–100 PPI is standard for desktop monitors at typical viewing distances. 140+ PPI gives noticeably sharper text. 220+ PPI is Retina-class.