If you are using one the the APS sensor cameras, and most people are, here is a conversion guide for you to figure out the crop factor for your lenses.
The conversion guide give you the working MM of a lens when put on a crop sensor body.
So for instance a 50mm lens when put in a cropped body is actually 80MM. A 600mm lens when put on a cropped body is 960mm. Most times it is not important what the MM’s are but if you do need to know this will help.
Some of the APS cameras that are available are:
Canon Rebel line, Canon 10D, 20D, 40D, 50D, 60D, 70D, 80D, 90D Canon 7D, 7D mk II with the 1.6 crop factor
Nikon D7200, Nikon D500, Pentax K3 and the Sony Sony A77 with 1.52 (I used 1.52 – there are some versions 1.53 or 1.54 but it gets to confusing to add all these)
(there are more brands and models but this is a sample)