How to Calibrate Your Screen
Calibration measures your screen's pixel density (DPI) so we can display objects at their true physical size. It takes about 10 seconds and only needs to be done once.
01
💳 Credit Card — Most Accurate
Recommended — works for any standard bank card or ID card
- Click Calibrate Screen in the bar above
- Place your credit card flat against your screen
- Drag the right edge of the blue guide to match your card's width exactly
- Click Apply This Calibration
Why this works: All standard credit cards are exactly 85.60 mm wide (ISO/IEC 7810 ID-1). Matching pixels to this known size gives us your exact DPI.
02
🖥️ Monitor Size
Useful if you don't have a card available
- Find your monitor's diagonal size (usually printed on the box or in specs)
- Click Calibrate Screen above
- Switch to the Monitor Size tab
- Enter your diagonal size in inches and click Apply
Note: May be less accurate on HiDPI/Retina displays due to CSS pixel scaling.
Frequently Asked Questions
Is the calibration stored permanently?
Yes — your calibration is saved to your browser's localStorage. It persists across visits until you reset it or clear your browser data. If you use a different browser or device, you'll need to calibrate again.
Why is my phone the wrong size?
Mobile browsers scale CSS pixels independently of physical pixels. Calibrating on a phone with a credit card gives the best result. Monitor diagonal input is not recommended on phones.
What DPI should my screen be?
Common values: 96 DPI (standard HD monitors), 109 DPI (27" 1080p), 163 DPI (standard Retina MacBook), 227 DPI (5K iMac). Your DPI is shown in the calibration bar after calibrating.
Can I use any card for calibration?
Yes — any standard credit card, debit card, driver's license, or government ID card. All follow the ISO 7810 ID-1 standard: exactly 85.60 × 53.98 mm.