Frequently Asked Questions
Find answers to common questions about our service
1How accurate is the online ruler?
Accuracy depends on calibration and zoom. Calibrate with a known reference (ID-1 card, A4 short edge, US Letter width, or a custom length) and keep browser zoom at 100% for the closest 1:1 scale. For critical work, verify with a physical ruler—screens and scaling can vary.
2Why does the scale change when I zoom or change display settings?
Browser zoom and OS display scaling change the on-screen pixel size, which breaks 1:1 measurements. Set zoom to 100%, avoid changing display scaling, and recalibrate after switching monitors, resolutions, or orientation.
3What units are supported?
You can measure in centimeters (cm), millimeters (mm), inches (in), and pixels (px). Pixel (px) readings are always available; cm/mm/in readings are based on your calibrated PPI. Switching units updates instantly.
4Can I convert pixels to inches or centimeters?
Yes, after calibration. Once your PPI is calibrated, px measurements can be estimated as inches or centimeters at a closer real-world scale. If you only need screen dimensions, px works without calibration.
5What are Guides and the Selection tool?
Guides add draggable lines for aligning edges on your screen. The Selection tool lets you drag a rectangle and read width, height, diagonal, and area in your selected units.
6Do you have device presets?
Yes. The calibration dialog includes PPI presets for common monitors, laptops, tablets, and phones. Presets are a quick starting point; fine-tune with a real reference when you need closer 1:1 measurements.
7Does this work on mobile?
Yes. It works in mobile browsers. For best results, calibrate on the same device (PPI differs per screen), keep zoom at 100%, and recalibrate after rotation or display setting changes.
8Is my data private?
Yes. The ruler runs locally in your browser. Calibration and preferences are stored on your device (local storage) so you don’t have to recalibrate every visit, and the app doesn’t upload images or measurement data.
9Why isn't my calibration saved?
Calibration is saved in your browser's local storage. It can reset if you clear site data, use private/incognito mode, block storage, or open the site in a different browser or profile.
Still have questions?
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