Frequently Asked Questions (FAQ)
Everything you need to know about measuring objects in centimeters, millimeters, and inches on computer monitors, smartphones, and tablets.
1. What is an online ruler?▼
An online ruler is a virtual measuring tool that runs directly in your web browser, allowing you to accurately measure small items in centimeters (cm), millimeters (mm), and inches at actual 1:1 scale without installing apps.
2. How do I use the online ruler?▼
Open the ruler on your phone or computer, place the object against the screen edge, align one end with 0, and read the measurement marks directly on your screen.
3. Is the online ruler free?▼
Yes, our service is 100% free with no registration, no downloads, and no hidden fees.
4. Can I measure in centimeters, millimeters, and inches?▼
Yes, switch between cm, mm, and inches (with 1/16" fractional divisions) with one click in the top toolbar.
5. Is there a 10 cm online ruler?▼
Yes! Most smartphone screens accommodate 10 cm to 15 cm, while laptops and desktop monitors can display 30 cm to 50 cm or more.
6. Does the ruler work on smartphones?▼
Yes, it works smoothly in any modern mobile browser (Safari, Chrome, Firefox) on Android and iOS.
7. Can I use the ruler on an iPhone?▼
Yes, open onlinelineyka.com in Safari on your iPhone. Our Retina display adaptation provides high precision out of the box.
8. How accurate is the ruler and how do I calibrate it?▼
For guaranteed 1:1 physical accuracy, calibrate using a standard payment card (exactly 85.60 mm wide) or select your screen diagonal in the Calibration Wizard.
9. Do I need to install an app?▼
No installation is needed. It launches instantly in your web browser, saving device memory.
10. Can I measure using the phone camera?▼
Placing small objects directly against a calibrated screen provides up to ±0.1 mm precision, avoiding lens distortion common with phone cameras.
Ready to Start Measuring?
Launch the free interactive 1:1 actual-size ruler and calibrate in seconds.