Reference Tools
Calibrated Screen Ruler
An on-screen virtual ruler. Calibrate it with a standard card for 100% accuracy on any display.
Virtual Ruler Calibration Guide
How do you calibrate an online ruler? Standard web pages cannot detect your physical monitor size or device pixels per inch (PPI). To make this virtual ruler accurate, place a standard credit card or ID card (standardized at exactly 3.37 inches or 85.6 mm wide) against your screen and adjust the slider until the bounding box perfectly aligns with the card.
Step 1: Align Your Calibration Card
Place any standard credit card, debit card, or driving license flat against your screen. Drag the slider or adjust the buttons below until the blue guideline box matches the card's width exactly.
Guideline Box
3.37" wide (85.6 mm)