DPI Calculator (PPI / Pixel Density)
Free DPI calculator: enter resolution and screen size to find pixel density (PPI/DPI), dot pitch and physical screen dimensions instantly with the formula shown.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
How the DPI Calculator Works
This calculator finds the pixel density of a screen — measured in PPI (pixels per inch) or DPI (dots per inch) — from its resolution and diagonal size. Enter the width and height in pixels and the diagonal screen size in inches, and it instantly returns the density, the dot pitch, and the physical width and height of the active display area.
The Formula
Pixel density is the number of pixels along the diagonal divided by the diagonal length in inches:
Diagonal (px) = √(width² + height²) PPI = Diagonal (px) ÷ Diagonal (inches)
Because a screen is a rectangle, the diagonal in pixels comes from the Pythagorean theorem. Once you know the PPI, two more values follow:
Dot pitch (mm) = 25.4 ÷ PPI Physical width (in) = width (px) ÷ PPI
Worked Example
For a 24-inch monitor at 1920 × 1080:
- Diagonal = √(1920² + 1080²) = √4,852,800 = 2,202.9 px
- PPI = 2,202.9 ÷ 24 = ≈ 91.8 PPI
- Dot pitch = 25.4 ÷ 91.8 = ≈ 0.2767 mm
- Physical size = 1920 ÷ 91.8 × 1080 ÷ 91.8 = ≈ 20.92 × 11.77 in
DPI vs PPI
The two terms describe the same idea from different industries:
- PPI (pixels per inch) is the screen term — how many pixels are displayed per inch.
- DPI (dots per inch) is the print term — how many ink dots a printer lays down per inch.
For calculating a monitor’s sharpness the math is identical, which is why both names are used for displays. True print DPI also depends on the printer’s hardware, not just resolution.
Why Pixel Density Matters
Knowing the PPI of a display helps you:
- Compare screen sharpness — two screens at the same resolution can look very different depending on size.
- Choose image export sizes — designers target a PPI so artwork is crisp on the intended device.
- Plan a workspace — a high-PPI screen viewed too far away wastes detail, while a low-PPI screen up close shows visible pixels.
| Screen | Resolution | Diagonal | Approx. PPI |
|---|---|---|---|
| Desktop monitor | 1920 × 1080 | 24 in | ≈ 92 |
| 27-inch 4K | 3840 × 2160 | 27 in | ≈ 163 |
| 16-inch laptop | 1920 × 1080 | 16 in | ≈ 138 |
| Smartphone | 2532 × 1170 | 6.1 in | ≈ 460 |
Frequently asked questions
How do I calculate the DPI of a screen?+
Find the diagonal resolution in pixels with √(width² + height²), then divide by the diagonal screen size in inches. For a 24-inch 1920×1080 monitor, √(1920² + 1080²) ≈ 2203 px, divided by 24 inches ≈ 91.8 PPI.
What is the difference between DPI and PPI?+
PPI (pixels per inch) describes how many pixels fit in an inch on a digital display, while DPI (dots per inch) is the printing term for ink dots per inch. For an on-screen calculation the math is identical, so the two terms are often used interchangeably for monitors.
What is a good DPI or PPI for a monitor?+
Around 90 to 110 PPI is standard for desktop monitors viewed at arm's length. Phones often exceed 300 PPI because they are held close, while 4K 27-inch displays reach about 163 PPI. Higher PPI means sharper text and smoother edges.
What is dot pitch and how is it related to DPI?+
Dot pitch is the distance between pixels, in millimetres. It is the inverse of pixel density: dot pitch = 25.4 ÷ PPI, since there are 25.4 mm in an inch. A higher PPI gives a smaller dot pitch and a sharper image.
Why does the same resolution look sharper on a smaller screen?+
Because the same number of pixels is packed into a smaller area, raising the pixel density. A 1920×1080 image is about 92 PPI on a 24-inch monitor but roughly 138 PPI on a 16-inch laptop, so the laptop looks crisper.