Online Ruler (cm, inch, px)
Measure on-screen lengths in centimeters, inches, or pixels. Calibrate with a credit card, A4 paper, US letter, or a custom length to match your screen. Calibration is saved locally in your browser.
Core Features
Made for on-screen measuring
Switch between cm/in and pixels, add guides, and calibrate when you need real-world scale.
- Screen Calibration
Use a known reference (card, paper size, or custom length) to adjust PPI for your screen. Recalibrate after zoom or display changes.
- cm / inch / px
Measure in centimeters, inches, or pixels. You can also show physical units and pixels together.
- Guides & Selection
Drag guidelines to check spacing, or draw a selection box to read width, height, diagonal, and area.
- Local by Default
No account needed. Calibration and preferences are stored in your browser (local storage).
About The Tool
What is Online Ruler?
Online Ruler is a screen ruler for quick on-screen measuring. It can show pixels, and it can estimate centimeters or inches after you calibrate your device. Without calibration, cm/in values use a default PPI and may be off.
Simple Steps
How to Use
- 1Calibrate
Open Calibrate and pick a reference (credit card, A4 paper, US letter, or custom length).
- 2Adjust
Adjust until the on-screen outline matches the real object. Keep browser zoom at 100%.
- 3Measure
Measure in cm, inches, or pixels. Use guides or the selection tool to check distances and sizes.
Benefits
Why Use This Ruler?
- Closer to Real Size
Calibration helps convert pixels to cm/in for your current device. Recalibrate after switching screens or changing zoom.
- Instant Access
No installation needed. This online ruler works on desktop, tablet, and mobile browsers.
- Privacy Focused
Calibration and settings stay on your device. The tool works without sending your measurements anywhere.
FAQ
Frequently Asked Questions
- It can be close after calibration. Without calibration, the cm/in display uses a default PPI and may be off. Keep browser zoom at 100% and recalibrate after display changes.
- Centimeters (cm), millimeters (mm), inches (in), and pixels (px). You can also show physical units and pixels together.
- Yes. It works on smartphones and tablets—calibrate on that device, and avoid browser zoom if you want cm/in to match your reference.
- Calibration and settings stay in your browser (local storage). The tool does not require you to upload images or measurement data.