Classes of License:
The Federal standard requires States to issue a CDL to drivers according to the following license classifications:
Class A -- Any combination of vehicles with a GCWR of 26,001 or more pounds provided the GVWR of the vehicle(s) being towed is in excess of 10,000 pounds.
Class B -- Any single vehicle with a GVWR of 26,001 or more pounds, or any such vehicle towing a vehicle not in excess of 10,000 pounds GVWR.
Class C -- Any single vehicle, or combination of vehicles, that does not meet the definition of Class A or Class B, but is either designed to transport 16 or more passengers, including the driver, or is transporting material that has been designated as hazardous under 49 U.S.C. 5103 and is required to be placarded under subpart F of 49 CFR Part 172 or is transporting any quantity of a material listed as a select agent or toxin in 42 CFR Part 73.
The above is from the federal CDL site. These are Federal Laws, the only difference from state to state in this is how strictly they enforce these. The more differences found state to state are in other requirements. And a whole new mess starts when you cross state lines or travel 150 airmiles from home.
In most any state, if you are getting paid to drive, example: if your driving for your job and you are on the clock, a commercial liscence of some type is required. (In Missouri it is a class E), And it makes no difference on what size of vehichle, you could be driving a car!