Converters & Time
Mobile ruler
A mobile-first online ruler with card calibration, manual tuning, centimeter/inch units, and horizontal/vertical marks.
Mobile ruler
Calibrate with a card and turn your phone into a centimeter or inch ruler.
Auto-estimated device scale：CSS 96dpi fallback
Auto-estimated; manual calibration available · 3.78 px/mm
Formula and method
After calibrating pixels per millimeter with an 85.60mm card width, the tool draws millimeter or 1/16-inch marks. Uncalibrated values are estimates.
Example
Example: place a card on the calibration block, adjust the slider until widths match, then measure small objects from the 0 mark.
Last updated:
FAQ
Is the mobile ruler accurate?
After calibration it is useful for everyday estimates. Use a physical ruler for official measurements.
Why calibrate with a card?
Most credit and transit cards are 85.60mm wide, making them easy reference objects.
Is data uploaded?
No. Calibration and drawing run in your browser.
Can it measure inches?
Yes. Switch between centimeter and inch marks.
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