Online Measure ruler | Measure Accurately and Easily
The Online Measure Ruler lets you measure objects on your screen accurately in inches or centimeters. Align your screen with the object for instant measurements on any device.
What Is an Online Ruler?
Hold a standard bank or ID card against your screen and drag the slider until the dashed box matches its width exactly. This sets the ruler to your real screen size.
How to Use the Online Ruler
The ruler measures real-world lengths using your screen, so it needs to know your exact screen size first. Calibrate once, then drag the ruler to measure.
- Select your device from the list, or use the credit-card slider to calibrate manually.
- Hold a standard credit card to the screen and match the dashed box to its width for the most accurate result.
- Switch between centimeters and inches with the unit button.
- Tap "Rotate ruler" to measure vertically, or "Full screen" for longer items.
- Drag the ruler left or right (or up and down) to read the distance shown below it.
Why Calibration Matters
Every screen has a different pixel density (DPI), so the same number of pixels can be a different physical size on each device. Calibrating with a known object such as a credit card (always 85.6 mm wide) or by selecting your exact device model tells the ruler how many pixels equal one centimeter, making on-screen measurements match a real ruler.
