Online Ruler - cm, mm, inches

Online Ruler will help you to take actual size measurements of any object in mm, cm, and inches. Also, it's free and easy to use.

Your current screen resolution is pixels.

Graduation of inch: "

Pixels per inch (PPI) :

(Set PPI according to your screen size)

About Online Ruler

Have you ever imagined that we can measure anything from Online Ruler? Now, you don't have to carry the physical ruler with you everywhere all the time. Just open our tool on any device and start measuring your object height, width, and length. Also, it allows you to take the measurements in millimeters, centimeters, and inches.

Try our other tools such as Notepad Online, Text to Speech, and Time Card Calculator.

Online Ruler - cm, mm, inches

How does it work?

The ruler showing on your computer or laptop screen is not an image. It takes your screen resolution automatically and adjusts according to your device screen. So, when you open this tool in a widescreen then it will extend to fill out the full screen. Also, it works fine on all large, medium, and small devices like smart TV, PC, laptop, mobile, and iPad.

How to Adjust the Virtual Ruler to Actual Size?

Our tool is convenient and it can also be calibrated to actual size to make the most accurate ruler online.

  1. Firstly, take any standard object whose length you already know. For example, smartphone, wallet, credit card, A4 size paper, or any paper money. These are the basic objects that you can find easily around you. Also, you can find the perfect size of these objects from Google.
  2. After that, place the object on the online ruler and compare the length. If the ruler does not show the correct length then adjust the PPI up and down till the ruler shows the correct result. When the object size matches the ruler size means your screen is calibrated successfully.
  3. Now you are ready to start measuring other objects. Also, you can save the PPI settings for next time use.

How to use Online Ruler?

It's very simple to use this virtual tool. But we recommend you do the calibration process before using it for very accurate results. Refer above section if you didn't do that.

  • For measuring, firstly, place the object near to the screen. Keep it such that you can see the scale. You can click on the ruler to mark a red line. So, after removing the object you can see the length clearly. This is how the measurements are done.
  • As mentioned before, the ruler has a mm, cm, and inch scale. The upper side of the ruler is mm and cm. The lower side shows an inch. Also, you can change the graduation of an inch. This option is just below the ruler. There are three graduations that you can choose: 1/8, 1/16, and 1/32. By default, it is selected to 1/16. When you change it to 1/32 then you can see the very small lines appear in between two inches. Therefore, using this feature, you can measure the smallest accurate size of the object.
  • Even more, you can change the Pixels per inch(PPI) to make the ruler more accurate and save it for future use. By default, it is set to "102.5".
  • Lastly, you can use the "Restore PPI" button to refresh all the settings.

Note: PPI numbers will be stored just on your web browser. Therefore, when you come back to the website then you don't need to change it again. It is stored until you don't delete the browser's cache and cookies.

Requirements for using the tool

  • Make sure that Javascript is enabled on your web browser.
  • Also, the browser should support the HTML5 canvas element in order to run the tool perfectly.
  • Make sure to tune the tool when your browser is at standard/default page adjustment.
  • Don't zoom in or zoom out on a web browser. Just keep it as default. Otherwise, you will get error in measurements.


Yes, of course, it is 100% accurate. Our tool works on pre-defined algorithms and it tracks your screen size when you open it. After that, it automatically adjusts the ruler scale as per the display size. As a result, you can see the wide, accurate, and full-width ruler.

You can calibrate it with any standard thing and adjust the PPI to make it correct.

As you can see that the inches scale is written at the bottom. So, read the bottom scale to check it.

Centimeters and millimeters are placed at the top part of the ruler. Therefore, read the top part to check it.

1 cm = 0.393701 inches

To convert the cm value into inches, just divide the centimeter value by 2.54.

Just open the on your mobile and start measuring.

There is a 30.48 cm in 12 inches ruler.

Final Words

Above all discussion was about the Online Ruler, how to calibrate to actual size, and how to measure any object using it. Also, it's free and easy to use. No login or signup required. You can access it through any web browser online. So, use it anytime and anywhere. Don't forget to share it with your friends.