Color management can be an interesting and challenging process when you want to maintain the same color no matter what application you're working with. In this instance, we want to convert an RGB to a Pantone in Photoshop. This is an easy task that will require only a few steps. Generally, any printed work should use Pantones, especially if the job will be performed by a commercial printer. RGB should be used for Web publishing.
Select the color you want to convert using the eyedropper tool located in the tool palette docked on the left. When you sample the color to be converted, it will appear in the "foreground color" square in the tool palette just below the eyedropper tool.
Double-click the square with the same color. That should open a new window in Photoshop called Color Picker (foreground color). In this window, you should see several color mode values related to the sample color, such as RGB and CMYK percentages used to create the sample color.
To view the Pantone number of the sample color, select "color libraries." This allows you to see the Pantone number you need. For example, RGB values R-10, G-50, B-75 have a Pantone of P2965C.