Pixel Density (PPI)

Turning Screen Size and Resolution Into a Pixel Density

Pixel density (PPI) measures how sharp a screen is by counting how many pixels fit within every inch of its physical size. Enter your screen’s diagonal size and resolution, and this calculator finds the PPI.

The Formula

$$\vC{\text{PPI}} = \frac{\sqrt{\vA{\text{Horizontal}}^2 + \vB{\text{Vertical}}^2}}{\text{Diagonal Size}}$$

where Horizontal and Vertical are the resolution in pixels, and Diagonal Size is in inches.

Worked Example

A 27-inch monitor with a resolution of 2560x1440:

1. $\vC{\text{PPI}} = \frac{\sqrt{\vA{2560}^2 + \vB{1440}^2}}{27} \approx \vC{108.8}$.

Key Factors to Consider

• How sharp a screen actually looks depends on both PPI and typical viewing distance, not PPI alone. A smartphone held close to the face needs a much higher PPI to look sharp than a large TV viewed from across a room — this is why phones commonly have far higher PPI ratings than TVs, even though a TV has many more total pixels.
• “Retina” and similar marketing terms describe a PPI threshold beyond which most people can no longer distinguish individual pixels at a typical viewing distance for that device type. There’s no single universal PPI number for this — the threshold depends on the assumed viewing distance, which is why the “sharp enough” PPI differs meaningfully between a phone, a laptop, and a TV.
• The same physical screen size can have very different PPI depending on its resolution. A 27-inch 1080p monitor and a 27-inch 4K monitor have identical physical size but very different pixel densities — PPI, not the diagonal size alone, is what actually determines how crisp text and images appear on screen.
• Higher PPI generally means sharper visuals, but also requires more processing power to render content at full resolution. This is part of why very high-PPI displays sometimes ship with upscaling or rendering techniques that don’t push every pixel natively, trading some processing overhead against battery life or performance.

Common Mistakes

• Comparing two screens’ sharpness by resolution alone, ignoring physical size. A 1920x1080 laptop screen and a 1920x1080 TV have the same pixel count but very different PPI, since the laptop packs those pixels into a much smaller physical area — resolution alone never tells you how sharp a screen actually looks.
• Assuming a single PPI number counts as “sharp” for every device type. A phone viewed a few inches from the eye needs a much higher PPI to look crisp than a TV viewed from across a room — there’s no one universal “good” PPI threshold, since it depends heavily on typical viewing distance for that device.
• Confusing a display’s native PPI with its rendered or scaled output. Some high-density displays render content at a lower effective resolution and upscale it for performance reasons, so the number this calculator reports (the display’s native pixel density) may not match the sharpness some content actually appears at.

Useful to Know

• Need to know a screen’s width-to-height proportions rather than its sharpness? Aspect Ratio Calculator calculates and simplifies a screen or image’s aspect ratio.
• Working with screen measurements in a different unit than inches? Unit Converter converts length, area, and other common units.