Question 1

Can I use my phone as a ruler?

Accepted Answer

Yes. The auto-detect feature identifies your phone model and calibrates the ruler to your screen's exact PPI. The ruler also works on tablets including iPad and other Android tablets. Place the object against the edge of your screen to measure.

Question 2

How accurate is this ruler?

Accepted Answer

Accuracy depends on calibration method. Credit card calibration is the most accurate at ±0.5%. Auto-detect is typically ±1%, and screen diagonal calibration is ±2%.

Question 3

What's the best way to calibrate?

Accepted Answer

For highest accuracy, use the credit card method. For convenience, auto-detect works great and requires no manual steps.

Question 4

How do I switch between cm, mm, and inches?

Accepted Answer

Use the unit buttons at the top of the ruler to toggle between centimeters, inches, and pixels. Your calibration stays the same when switching units.

Question 5

Can I use my camera as a ruler?

Accepted Answer

Camera-based measurements are unreliable due to lens distortion and perspective errors. This tool uses a more accurate screen-based approach instead.

Question 6

What devices does auto-detect support?

Accepted Answer

Auto-detect covers over 130 devices including Apple, Samsung, Google Pixel, Xiaomi, OnePlus, Microsoft Surface, and common monitor sizes.

Question 7

How do I read the measurements?

Accepted Answer

The largest marks with numbers are whole units. In centimeter mode, smaller lines represent millimeters. In inches mode, subdivisions represent fractional inches.

Question 8

Is this tool free to use?

Accepted Answer

Yes, completely free. No account required, no data collected, no ads that interfere with measuring.

Question 9

Which browsers are supported?

Accepted Answer

The ruler works on Chrome, Safari, Firefox, Edge, Opera, and Samsung Internet across desktop and mobile.

Question 10

Why is calibration necessary?

Accepted Answer

Every screen has a different pixel density. Calibration tells the ruler your screen's actual PPI so it can render tick marks at real-world scale.

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