Let’s consider this a useful tool in Adobe Photoshop View-Rulers. The ruler allows you to accurately set the size of the document and its individual elements. Also, in Photoshop there is a setting options to display line – for example, you need instead of pixels to put millimeters or centimeters, etc.
The measurements in Photoshop or how to draw a line in Photoshop

To turn on rulers in Photoshop, we need to go to menu View-Rulers . Also note the other menu items, for example, such as Snap. Using this function you can bind line:
Document Bounds
To display the grid, as well as the convenience of affixing the guide, turn it in View-Show-Grid. Do not forget to use hot keys – they will make it easier to access menu and speed up the editing process (on our website there is a separate item, where you can see keys for details).
After turning on the grid, you should see more data on the screen. Agree to bind the guides will now be much easier.
This is done (on rails) through the menu or by pressing CTRL + ;.
Now in the settings menu line, press right-click to run the selection function parameters. To do this, simply press CTRL + R. Here you can select what will be measured your space and the current document (units) – these are pixels, inches, centimeters, millimeters, points, picas (4.23333333 mm), percent.
To measure the distance of a particular fragment in an image, we need a tool Ruler Tool. All that is necessary is to draw a line in the desired direction and look at the results at the top of the screen (control panel tool).
Measurements are given in the format which we set earlier (see the bit above about the units).
You can turn off the grid by clicking again on the menu – so your eyes will not get tired from the constant ripple.

The measurements in Photoshop or how to draw a line in Photoshop