I have listed 7 free online rulers in cm, mm, and inches. It uses your monitor pixels per inch (PPI) to display the actual size of the ruler, with high accuracy.
This is an online vitrual ruler (mm,cm,inches) that can be adjusted to an actual mayancalendaronline.info measures the size of your screen.
Click on the image above to view this ruler in actual life size. This actual size online ruler shows inches and metric (centimeter and millimeter). Want to see more.