Actual Size Online Ruler

Welcome to the most accurate virtual ruler on the web. Our tool allows you to measure any object in Centimeters (CM), Millimeters (MM), or Inches (IN) with 100% precision by syncing with your screen's unique pixel density.

Quick Calibration Guide

Since every screen is different, calibration is required for "Actual Size":

  1. Grab a standard Credit Card or ID card.
  2. Click the blue "Calibrate My Screen" button.
  3. Place your card on the screen and drag the box corner to match its size.
  4. Save, and your ruler is now perfectly scaled to your hardware.

Frequently Asked Questions

Q: Why isn't the ruler accurate by default?

A: Browsers know your resolution (e.g., 1920px), but they don't know the physical size of your monitor (e.g., 24 inches). Without this knowledge, 1 inch on a phone would look huge compared to 1 inch on a TV. Calibration bridge this gap.

Q: What is the standard card size used?

A: We use the international ID-1 standard (ISO/IEC 7810), which is 85.60 mm × 53.98 mm (3.370 in × 2.125 in). This applies to almost all bank cards and driver's licenses.

Q: Will this work on mobile devices?

A: Yes! Our ruler is responsive. It detects the high-density "Retina" displays of modern smartphones and adjusts its initial guess accordingly.

Screen Calibration

Adjust the box to match a physical credit card. This ensures 100% actual size accuracy.