Online Ruler
Measure objects on your screen with precision. Calibrate for accurate measurements in centimeters, millimeters, or inches.
Current Scale: 1px = 0.265mm (96 DPI)
📐 Reference Objects for Calibration
✨ Key Features
Everything you need for accurate on-screen measurements
Multiple Units
Switch between centimeters, millimeters, and inches instantly
Easy Calibration
Calibrate using common objects like credit cards or A4 paper
Dual Orientation
Switch between horizontal and vertical ruler modes
Zoom Control
Zoom in or out for precise measurements of any size
Mobile Friendly
Works perfectly on desktop, tablet, and mobile devices
Completely Free
No registration, no limits - use as much as you want
🎯 Perfect For
Discover how different professionals use our online ruler
Designers & Developers
Measure UI elements, check spacing, and verify dimensions in web and app designs
Students & Teachers
Quick measurements for homework, projects, and online learning activities
Crafters & DIY Enthusiasts
Measure materials and plan projects when a physical ruler isn't handy
Home & Office
Quick measurements for everyday tasks without searching for a physical ruler
❓ Frequently Asked Questions
Everything you need to know about using the online ruler
How accurate is the online ruler?
The accuracy depends on your screen's DPI (dots per inch) and calibration. After calibrating with a known object like a credit card, measurements are typically accurate within 1-2mm. Different screens and zoom levels can affect accuracy, so calibration is recommended for precise measurements.
How do I calibrate the ruler?
Click the "Calibrate" button or select a reference object (like a credit card). Place the physical object on your screen and adjust the ruler until it matches the object's actual size. The tool will remember your calibration for future use.
Why do I need to calibrate?
Different screens have different pixel densities (DPI/PPI). A 15-inch laptop and a 27-inch monitor display pixels at different physical sizes. Calibration ensures the ruler matches real-world measurements on your specific screen.
Does browser zoom affect measurements?
Yes, browser zoom (Ctrl/Cmd + or -) will affect accuracy. The tool detects zoom changes and displays a warning. For accurate measurements, keep your browser at 100% zoom or recalibrate after changing zoom levels.
Can I use this on my phone or tablet?
Yes! The online ruler works on all devices. Mobile devices typically have higher pixel density, so calibration is especially important. Use a known object like a credit card to calibrate for accurate measurements on your device.
What's the difference between cm, mm, and inches?
Centimeters (cm) and millimeters (mm) are metric units (1 cm = 10 mm). Inches (in) are imperial units (1 inch = 2.54 cm). Choose the unit that matches your needs or regional preference.
⭐ What Users Say
Join thousands of satisfied users who rely on our online ruler
"Super handy for checking UI element sizes in my designs. The calibration feature works perfectly, and I love that I can switch between cm and pixels easily."
"I use this all the time for my craft projects! No more searching for my physical ruler. The credit card calibration is genius - so simple and accurate."
"Perfect for teaching online! My students can measure objects at home during virtual classes. Works great on tablets and phones too."
Based on 1,523+ user reviews
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