Are you desperately looking for a physical ruler to measure things, but can’t find one? Don’t worry. There are plenty of free virtual rulers on the Internet. Here are some websites that provide online virtual rulers in both metric (cm and mm) and inches (in).
Calibration of these rulers are normally done in 3 different ways: by referring to your monitor pixels per inch (PPI), by comparing the size of common objects, or by referring to your screen size in inches. Therefore, I have arranged the list according to their calibration methods. Do note that online rulers are generally not as accurate as physical rulers, especially online rulers that are calibrated according to your screen size.
Recommended reading: How To View The Actual Size Of Items On Screen
Monitor PPI
Actual Size Ruler
The most accurate online ruler in this list. It uses your monitor pixels per inch (PPI) to display the actual size of the ruler, with high accuracy. Here is a PPI calculator to calculate your monitor PPI. Actual Size Ruler also allows you to adjust the graduation of an inch on the ruler.
Compare To Common Objects – bank card, banknote, etc.
PiliApp Online Ruler – cm | inch
You can move the ruler freely on your screen by selecting “drag it”. Also, if you are not really sure about your monitor size, PiliApp has a comparing tool to help you.
Sylen’s Online Ruler
LifeSizer Online Ruler
Screen Size
MyOnlineRuler
Apart from the online ruler, MyOnlineRuler also has an online ruler for iPhone (by displaying the ruler vertically), printable rulers in different colors and sizes, and a pixel ruler to measure objects in pixels.
iRuler
RulerOnline.net