PPI Calculator (Pixels Per Inch)

This PPI calculator computes the pixel density of a display from its resolution and diagonal size.

Formula notes

PPI = √(width² + height²) / diagonal inches.

Worked examples

1. Example: a 27″ 2560×1440 monitor gives √(2560² + 1440²) / 27 ≈ 108.8 PPI.
2. A 27-inch 3840 x 2160 display has a pixel diagonal of about 4405 pixels and density near 163 PPI.

How to use it

1. Enter the horizontal and vertical resolution.
2. Enter the diagonal size in inches.
3. Read the pixel density in PPI.

Frequently asked questions

Limits and interpretation

• The calculation assumes the advertised diagonal is the active rectangular image area and pixels are square.
• Perceived sharpness also depends on viewing distance, vision, scaling, subpixel layout, contrast, and content.

References

• NIST: SI Units