Pixels per Inch (PPI)
Drag the corner of the outline to fit a real bank or credit card (85.6 mm wide)
– PPI
How many pixels fit along one physical inch of the screen.
Drag the corner of the outline to fit a real bank or credit card (85.6 mm wide)
Calibrate with any credit card to discover your screen's true pixels-per-inch — then use the result to size UI elements to real-world millimetres or inches.
Last updated: February 2026
Place a standard bank card, credit card, or ID card flat against your screen. Drag the corner handle until the dashed outline matches the card's width exactly. All ISO/IEC 7810 ID-1 cards (Visa, Mastercard, driving licences) are 85.6 mm wide, so the tool uses that reference to calculate your display's true PPI.
The PPI value updates live as you drag. Click Copy PPI to save the number for your design tool, spec sheet, or bug report. This calibration works regardless of browser zoom because you're matching a physical object to the screen.
PPI (pixels per inch) measures pixel density — how many pixels fit along one physical inch of your screen. A higher PPI means smaller, more tightly packed pixels, which produces sharper text, crisper icons, and smoother curves.
Two monitors can have the same resolution (say 1920×1080) but very different PPI values. On a 24-inch monitor that resolution gives about 92 PPI — fine for desktop use. On a 15.6-inch laptop it jumps to about 141 PPI — noticeably sharper. On a 6.1-inch phone (at the same pixel count, though most phones exceed it) you'd get over 360 PPI, where individual pixels become invisible to the naked eye.
Apple coined the term "Retina" for displays with a PPI high enough that the human eye cannot discern individual pixels at a normal viewing distance — roughly 220+ PPI for a laptop and 300+ PPI for a phone held at arm's length.
| Device | Resolution | PPI |
|---|---|---|
| iPhone 16 Pro (6.3") | 1206×2622 | ~460 |
| Samsung Galaxy S25 Ultra (6.9") | 1440×3120 | ~505 |
| MacBook Pro 14" (2024) | 3024×1964 | ~254 |
| Dell 27" 4K (U2723QE) | 3840×2160 | ~163 |
| Apple Studio Display (27") | 5120×2880 | ~218 |
| LG 32" 4K (32UN880) | 3840×2160 | ~140 |
| iPad Pro 13" M4 | 2064×2752 | ~264 |
If you know your screen's resolution and physical diagonal size, you can calculate PPI with this formula:
PPI = sqrt(width_px² + height_px²) / diagonal_inches Example: 27-inch 4K monitor PPI = sqrt(3840² + 2160²) / 27 PPI = sqrt(14,745,600 + 4,665,600) / 27 PPI = 4,406.08 / 27 PPI ≈ 163.2
This gives the exact same number shown in the device table above. The credit-card calibration method on this page is useful when you don't know the exact diagonal measurement or when OS-level scaling makes the reported resolution unreliable.
PPI (pixels per inch) refers to screen displays — it measures how densely pixels are packed. DPI (dots per inch) refers to print — it measures how densely ink dots are placed on paper. The terms are often used interchangeably in casual conversation, but they describe different things.
A web image at 72 PPI and a print file at 300 DPI can have the same pixel dimensions, but the print version will appear physically smaller because each pixel maps to a tinier area on paper. When designing for screens, think in PPI and CSS pixels; when designing for print, think in DPI and physical dimensions (mm or inches).
Check your display's colour depth and gamut alongside PPI to understand the full capability of your screen.
For a desktop monitor viewed at 60–80 cm, 110 PPI or higher delivers sharp text. For a laptop at arm's length, 150+ PPI is ideal. For phones held at 25–30 cm, 300+ PPI makes pixels invisible — which is why most flagship phones exceed 400 PPI.
PPI measures pixel density on screens; DPI measures ink-dot density in print. They are conceptually similar (density per inch) but apply to different mediums. For screen work, PPI is the correct term.
Beyond a certain point (roughly 200 PPI at desktop distance, 350 PPI at phone distance), the human eye can no longer distinguish individual pixels. Higher PPI past this threshold offers diminishing returns but can still benefit VR headsets, where the screen is centimetres from your eyes.
Operating systems often assume a standard PPI (typically 96 on Windows, 72 on macOS) for scaling purposes, regardless of the actual panel density. This tool measures the true physical PPI by calibrating against a known real-world object (the credit card).
Yes. On phones, use a credit card held against the screen and drag the handle with your finger. The calibration works the same way — the card's width is always 85.6 mm regardless of the device.