XotkaOnline Ruler (cm, mm, inch)
Measure small objects against your screen in centimetres, millimetres or inches.
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About Online Ruler (cm, mm, inch)
An on-screen ruler is only accurate if it matches your display's real pixel density. Calibrate it using a known object such as a bank card before you measure. Treat results as approximate; use a physical ruler for anything critical.
How to use this tool
- Calibrate the ruler using a card or object of known size.
- Hold the object against the screen and line up one edge with zero.
- Read the measurement in cm, mm or inches.
Results and supported features can vary by tool and input. Review the controls and any on-page notes before relying on an output.
Frequently asked questions
How accurate is an online ruler?
It can be close after calibration, but it depends on your screen and browser zoom. Use a physical ruler for precise work.
Why do I need to calibrate it?
Screens have different pixel densities, so without calibration the on-screen centimetre may not equal a real centimetre.
Does browser zoom affect it?
Yes. Reset zoom to 100% and recalibrate if you change it.