How it works
Complete the job in three clear steps
- Add a card-width calibration or display DPI.
- Choose the relevant options and create a calibrated on-screen ruler.
- Review the result, then copy or download it when available.
Free private browser tool
Online Screen Ruler
Calibrate a horizontal screen ruler against a physical card, then measure in millimetres, centimetres, or inches.
Free to use Your input and result stay in this browser. Lucaden does not upload them.
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Important
Check the result before relying on it
Review generated output before using it in production. Formatters and converters can validate structure, but they cannot understand every application-specific rule or guarantee that transformed content has the intended meaning.
Practical details
What this Lucaden tool does
Calibrate a horizontal screen ruler against a physical card, then measure in millimetres, centimetres, or inches.
This dedicated Lucaden route runs on the current device and reuses a reviewed local engine where an equivalent Lucaden capability already exists.
Included capabilities
- Payment-card calibration
- DPI calculation
- Metric and inch scales
- Responsive overflow
Useful for
- Estimate a small object
- Check a print mockup
- Compare CSS pixels
- Teach measurement conversion
Questions
About this tool
Is an online ruler exact?
Only after careful calibration, and even then browser zoom, display scaling, perspective, and panel hardware introduce error. Use a physical calibrated instrument for important measurements.
How do I calibrate it?
Set browser zoom to 100%, hold a standard 85.60 mm payment-sized card against the calibration bar, and adjust the pixel width until both match.
Open-source foundations
Built transparently
Lucaden documents its standards sources, architectural references, and permissive runtime dependencies while keeping this workspace consistent with the Lucaden interface.