DPI to PPI Converter Formula
Understand the math behind the dpi to ppi converter. Each variable explained with a worked example.
Formulas Used
Pixels Per Inch (PPI)
ppi = diagonal_inches > 0 ? diagonal_px / diagonal_inches : 0Pixel Size
pixel_size = diagonal_inches > 0 ? 25.4 / (diagonal_px / diagonal_inches) : 0Total Pixels
total_pixels = width_px * height_pxVariables
| Variable | Description | Default |
|---|---|---|
width_px | Screen Width(px) | 1920 |
height_px | Screen Height(px) | 1080 |
diagonal_inches | Diagonal Size(inches) | 24 |
diagonal_px | Derived value= sqrt(pow(width_px, 2) + pow(height_px, 2)) | calculated |
How It Works
Screen PPI Calculation
PPI = sqrt(W² + H²) / Diagonal Inches
Where W and H are the pixel dimensions.
Common Screen PPI
Worked Example
1920x1080 display, 24-inch diagonal.
width_px = 1920height_px = 1080diagonal_inches = 24
- 01Diagonal pixels = sqrt(1920² + 1080²) = 2203
- 02PPI = 2203 / 24 = 91.8 PPI
- 03Pixel size = 25.4 / 91.8 = 0.277 mm
Frequently Asked Questions
What PPI is considered "Retina"?
Apple defines Retina as a PPI where individual pixels are indiscernible at typical viewing distance. For phones (held close), this is ~326+ PPI. For laptops (~18 inches away), ~220+ PPI. For desktops (24+ inches), ~110+ PPI.
Is higher PPI always better?
Higher PPI means sharper text and images but also requires more GPU power and makes UI elements smaller unless scaled. For most desktop use, 100-163 PPI is comfortable.
Ready to run the numbers?
Open DPI to PPI Converter