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Usage Guide
2026-08-14
3 min read

Step-by-Step Guide to Calibrating and Using an Online Screen Ruler

Step-by-step instructions for zero-error calibration and using multi-marker measurements directly in your web browser.

1. 3-Step Calibration Procedure

  1. Verify Browser Zoom: Press Ctrl + 0 (or Cmd + 0 on Mac) to reset display zoom to 100%.
  2. Select Calibration Mode: Click [Calibrate] in top bar and select either [Credit Card] or [Monitor Size].
  3. Align Physical Reference: Hold a physical credit card against screen, adjust container width to match 85.60 mm width, and save.

Start Measuring Objects Now!

Calibrate in 1 second and measure real-world items on your screen in cm or inches.

Open Online Ruler