Place a standard credit card (or any card matching ISO/IEC 7810 ID-1 dimensions: 85.6 × 53.98 mm) on the screen. Use the calibration screen to align the on-screen outline with your physical card. This ensures measurements are accurate for your specific device screen.
Calibration is saved automatically and persists between sessions.
RulerApp supports the following measurement units:
You can switch between units at any time using the unit toggle in the app.
After calibration, RulerApp provides measurements accurate to within approximately ±0.5 mm. Accuracy depends on proper calibration — if measurements seem off, try recalibrating with a credit card.
Note that screen-based rulers are intended for quick reference measurements and may not replace precision instruments for professional use.
Yes, RulerApp works on both iPhone and iPad. Each device needs to be calibrated separately since screen sizes and pixel densities differ between devices.
On iPad, you benefit from a larger measuring surface, allowing you to measure longer objects without repositioning.
Drag the markers (start and end points) along the ruler to measure a specific segment. The distance between the two markers is displayed in your selected unit.
This is useful when measuring objects that don't start at the edge of the screen, or when you need to measure a specific portion of an object.
Yes, completely private. RulerApp stores only calibration settings and unit preferences on your device. The app does not connect to any server, contains no analytics or tracking SDKs, and transmits no data anywhere.
See our Privacy Policy for full details.
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