A free virtual ruler for your screen. Measure in centimetres or inches with optional calibration for accurate results.
Select centimetres or inches using the toggle buttons above the ruler.
Place a credit card (85.6mm / 3.37in wide) on screen and adjust the slider until it matches the ruler exactly.
Place the object against the ruler on your screen and read the measurement directly.
The ToolCentrix Online Ruler is a free virtual ruler that displays directly on your screen, allowing you to measure objects in centimetres and inches without a physical ruler. It uses your screen's pixel density (PPI) to calculate accurate measurements and includes a calibration slider for fine-tuning.
How screen rulers work: Every screen has a pixel density measured in pixels per inch (PPI). By knowing this value, a browser can draw a ruler where each centimetre or inch corresponds to the correct number of pixels. The default PPI is set to 96 (a common standard), but your screen may differ, which is why calibration is important.
Calibrating for accuracy: The most reliable calibration method is to use a standard credit card, which is exactly 85.6mm (3.37 inches) wide. Place the card against the ruler on your screen and drag the slider until the ruler matches the card's width precisely. This calibration corrects for any differences in your screen's reported pixel density.
Use cases: The online ruler is useful for quickly measuring small objects like phone screens, books, paper sizes, envelopes, or craft materials when you don't have a physical ruler nearby. It is also useful for web designers and developers who want to measure UI elements on screen.
Limitations: The online ruler is not a substitute for a precision measuring instrument. For engineering, medical, or legal measurements requiring certified accuracy, always use a calibrated physical ruler or measuring device.
ToolCentrix Online Ruler is completely free, works in all modern browsers, and requires no downloads or installation.