The Online Ruler Tool is a simple and accurate way to measure objects directly from your screen. It allows users to measure in centimeters (cm), millimeters (mm), and inches without needing a physical ruler. This tool is useful for students, designers, and anyone who needs quick measurements.
How the Online Ruler Works

Online Ruler shows a virtual ruler on your screen that you can use to measure objects by placing them on the screen. It works with three different units: centimeters, millimeters, and inches. To get accurate results, you may need to calibrate the ruler by adjusting the scale to match your screen size. Select your device from the list or enter the size of your screen diagonal in inches.We have added the most popular devices to the list. (All devices have different pxels per inch – read more about PPI here).
Online Ruler Features
- Multiple Measurement Units: Supports cm, mm, and inches.
- Easy Calibration: Choose your device from the list.
- Works on Any Device: Accessible on computers, tablets, and smartphones.
- No Installation Needed: The tool runs directly in your web browser without requiring downloads.
Who Use an Online Ruler?
A digital ruler is a convenient tool that helps measure objects accurately without needing a physical ruler. Here’s why it’s useful:
- For Design & Creativity – Graphic designers, digital artists, and UI/UX professionals often need precise measurements. The online ruler makes it easy to check dimensions quickly.
- For Students & Teachers – Whether for geometry, science projects, or classroom exercises, an online ruler is a great tool for students learning about measurements.
- For Everyday Use – Need to measure paper, a small object, or even your screen size? This ruler is accessible anywhere, making it perfect for quick, on-the-go measurements.
How to Get the Most Accurate Measurements
To ensure accuracy, follow these tips:
- Calibrate your ruler – Because screen sizes vary, calibration is key. You can do this by comparing the online ruler to a physical one, or by adjusting it based on your display settings.
- Use the correct display settings – Make sure your browser zoom is set to 100% for the most accurate results.
- Choose the right unit – Easily switch between centimeters, millimeters, and inches for the most relevant measurement.
By following these steps, you’ll get accurate and reliable measurements every time.