Read · compare · verify
Reading guide
Worked example5 cm = 50 mm; choose the edge that has enough physical span
| Reading | Equivalent | How to read it |
|---|---|---|
| 1 cm | 10 mm | Small paper or craft comparison |
| 2.54 cm | 1 in | Exact metric/imperial reference |
| 5 cm | 50 mm | Check the active edge before measuring |
| 10 cm | 100 mm | May require the vertical span |
Measure without a hover pointer
Choose a vertical or horizontal edge, then gently align one end of a small, flat object with the scale’s origin. Tap the other endpoint to pin a guide. Drag the guide to adjust its position; tap it to remove it. The left edge is active initially because a portrait phone usually offers more measuring space vertically than horizontally. The target input can also pin a known length without requiring precise finger placement.
Check what fits on this screen
The fit readout uses the current measuring area and calibration to estimate its horizontal and vertical physical spans. Browser controls can reduce the usable area, even on a large phone. If your requested length does not fit, the tool warns you instead of compressing it. Try a different edge or orientation and recheck the calibration. For an object longer than the screen, use a physical ruler or tape measure.
Calibration and careful handling matter
Auto-detection is a convenience, not proof that the model or screen density was identified correctly. If the outline is too wide to fit, switch the card calibration to its vertical orientation. Hold any reference gently near the screen; do not press hard, use sharp objects, or expose the device to liquids. The tool does not ask for camera access and cannot measure a room, a person’s height, or a distant object through the camera.
How this ruler works
The scale uses your current calibration in CSS pixels per inch. Metric ticks divide that density by 25.4; inch ticks divide it by 16. Conversions use the exact definition 1 inch = 25.4 mm. The target keeps its entered length rather than stretching to fill the display.
Keep browser zoom at 100%, verify with a known reference, and recheck after changing screens. Inputs stay in your browser; no camera, account, or upload is required. For critical dimensions, use a suitable calibrated physical instrument.
Methodology, calibration help, and measurement support: Accuracy methodology · Calibrate screen · Contact us. Unit definitions: NIST.