on-screen measuring tool in inches/centimeters


⬇ Specify your screen size

If you want to measure the actual size of a small object in inches or centimeters, and there is no real ruler at hand — this virtual on-screen online ruler will help you. You can make the necessary measurements on any device that allows you to browse the web — this online app works both on computers with a large screen (laptops, PC monitors, monoblocks or smart TVs) and mobile gadgets (phones, phablets, tablets, e-ink readers). The maximum length of the ruler (fully visible when it is displayed on a sufficient screen) is 20 inches, or 50 cm (500 mm) for metric scale option.

💁 How to use the online ruler

Attention: for correct display of the ruler (in proportion to the actual physical length), it must be calibrated. You can calibrate it in one of two ways:

  1. 📱 💻 📺 Set screen diagonal

    The most reliable and easy way. Specify the size of the diagonal of your screen in inches (") - enter its value in the input field located in the lower left corner of the ruler image, then click the or press the button on the keyboard. You can also select the size from the drop-down list (which opens when you click the button , that is adjacent to the numeric input field), which presents many of the most common options among users.

    Here is the diagonal of the current device's display, automatically detected by the browser: . This calculated value in most practical cases does not correspond to its real extent and is proposed for consideration as an approximate one. This circumstance is caused by the existing constraint imposed by the specifics of the interaction of modern web browsers (none of which has the functionality of providing web applications with access to information about the physical parameters of the display) with operating systems. Depending on the type and class of device, the probable error varies in a range of up to several centimeters, or 1 inch - accordingly, to the best of its degree, the reliability of the indications of the uncalibrated online ruler will differ from the standard on. Nevertheless, the deviation may be minimal - in this case the initially visualized ruler will be suitable for measurements that do not require high accuracy (especially when measuring small objects).

    If you do not know the exact value of the diagonal of your screen, you can find in the technical documentation attached to the device, or simply search on the Internet by the model name.
    If, for some reason, this information is difficult to obtain and you have standard plastic card with you, you can resort to the second method. ↓

  2. 💳 Fit to the width of the plastic card

    You can also calibrate the on-screen ruler by using a bank payment card - its standard width is 3.37 inches (3 3⁄8 in), or 85.6 mm (8 centimeters 56 millimeters) as metric. For your convenience, the corresponding sign is plotted under the scale of the ruler. Change the diagonal value in the input field until the edge of the plastic card attached (oriented horizontally) to the screen coincides with the black stroke left to the icon.

    Thus, using this method at the same time will allow to determine the size of the display diagonal. In order to avoid the known inconvenience associated with the selection of a number by successive manual input, bring it to the desired value using the vertical scroll arrows appearing on the right side of the input field when you hover the cursor over it (when using the virtual ruler on the PC).

📏🔧 ️️ How the actual size of the ruler is achieved

  1. Based on browser-defined screen height and width, the script calculates the diagonal in pixels (it does not matter if the number of virtual pixels that the browser operates on is the actual physical resolution of the display);
  2. calculates PPI (pixels per inch) of the screen: the resulting diagonally expressed diagonal is divided by the user's diagonal value in inches;
  3. determines the length of the ruler in pixels, the corresponding real 50 centimeters: PPI value is multiplied by expressed in inches 50 cm. For inch scale is is just multiplied by 20.

⚠️ ️Note

It should also be borne in mind that the foregoing is only true when: