Phone ruler
The initial scale is a CSS 96dpi estimate; align an 85.60 mm standard card and explicitly confirm calibration.
Estimated scale
The initial CSS 96dpi scale is only an everyday estimate. Align a standard card first.
Screen zoom and card placement introduce error; use a physical ruler for formal measurement.
How to use this tool
Start with a CSS 96dpi estimate, align the on-screen reference card to 85.60 mm, and explicitly confirm before the current screen is calibrated.
Display centimeter or inch marks to estimate small objects. Accuracy depends on your physical reference, screen and calibration; actual-size accuracy is not guaranteed.
💡 3 Quick Steps to Get Started
Use a reference verified to be 85.60 mm wide. Adjust the scale slider to match the outline, then confirm calibration. Not every card has this width.
Choose centimeters or inches, vertical or horizontal, and left or right edge. Marks occur every 1 mm or 1/16 inch.
Align with zero and read the estimate. For example, 1 centimeter is 10 mm; the visible screen limits measurable length.
When it helps
Use centimeter/inch, horizontal/vertical, and left/right controls; a viewport, orientation, or meaningful screen-density change makes calibration stale.
How it works
Adjust the on-screen reference to an ISO/IEC 7810 ID-1 card width of 85.60 mm, then confirm px/mm. The unconfirmed initial scale is only an estimate.
Worked example
Place an 85.60 mm card over the reference, adjust and confirm it, then estimate a small object from zero; recalibrate after rotating the phone.
Limits and data handling
Browser zoom, screen protectors, card placement, and device rendering introduce error. Use it only for everyday estimates and use a physical ruler for formal measurement.
Scale, orientation, and calibration state remain in the current browser page and are not uploaded or retained; analytics excludes calibration and measured values.
Screen Ruler Calibration and Estimated Measurements
Screen Ruler Calibration and Estimated Measurements
Display centimeter or inch marks to estimate small objects. Accuracy depends on your physical reference, screen and calibration; actual-size accuracy is not guaranteed.
Use a reference verified to be 85.60 mm wide. Adjust the scale slider to match the outline, then confirm calibration. Not every card has this width.
Choose centimeters or inches, vertical or horizontal, and left or right edge. Marks occur every 1 mm or 1/16 inch.
Align with zero and read the estimate. For example, 1 centimeter is 10 mm; the visible screen limits measurable length.
The initial scale is estimated. Recalibrate after scale, viewport, orientation or pixel-density changes; Reset restores the estimate.
Calibration stays in current page memory. Do not use for measurements requiring certified precision; keep sharp objects off the screen.
Feedback
How can we improve this tool?
Send a suggestion or bug report for this tool.
FAQ
What inputs does Phone ruler accept?
No file is needed. Use an ISO/IEC 7810 ID-1 card that is 85.60 mm wide as the manual reference; the initial CSS 96dpi value is an estimate.
How does Phone ruler produce its result?
Calibration becomes valid only after the user aligns the card and presses confirm. A viewport, orientation, or meaningful screen-density change marks it stale.
What limitations apply to Phone ruler?
Browser zoom, screen protectors, card placement, and device rendering introduce error. Use it only for everyday estimates and use a physical ruler for formal measurement.
How does Phone ruler handle data?
Scale, orientation, and calibration state remain in the current browser page and are not uploaded or retained; analytics excludes calibration and measured values.
