What license you need depends on a number of factors, namely,the vehicle's use, the Gross Combined Weight Rating of the towvehicle and of the trailer, and the Gross Combined Weight Rating ofthe two.For usage, is the vehicle for a business or commercial venture?If so, it's regulated as a commercial vehicle. Private use, thereare two possibly applicable exemptions for CDL requirements here-Recreational Vehicles - when operated for not-for-hire, personaluse, these are exempt from requiring a CDL. Now, on a for hirebasis, such as hired drivers, or transporters, then they're treatedthe same as any other commercial vehicle.Farm vehicles - when registered as such, when operatedexclusively for the purposes of that farm (no third party for hireusage), operated within a 150 road/100 air mile radius of the farm,and operated by the farmer, immediate family members of the farmer,or direct (W2/W4, not 1099) employees of the farmer.Non-commercial vehicles which don't fall under those exemptionscan be a bit of a grey area, as many states put commercial plateson pickup trucks used for private use.So, if it does fall under the criteria of a commercial usevehicle, the length of the trailer has nothing to do with thelicense required - it's weight.So now we get into Gross Vehicle Weight Rating. This is themaximum loaded weight the vehicle is rated to run at - a 33,000 lb.GVW vehicle might only weigh 16,000 lbs. empty, but it's treated asa 33,000 lb. vehicle at all times.Gross Combined Weight Rating is the combined weight rating ofall portions of the combination - so, for example, a truck with a10,000 lb. Gross Vehicle Weight Rating with a trailer which has a16,000 lb. GVWR comes to a total Gross Combined Weight Rating of26,000 lbs.So.. there are three classes of CDL. The 'lowest' being Class C.Class C covers single vehicles with a Gross Vehicle Weight Ratingof up to 26,000 lbs., and is used for instances where such vehicles- which normally don't require a CDL - would, such as any vehiclehauling a quantity of hazardous material which requires placards tobe displayed under CFR49 regulations, or a commercial or school busdesigned to transport more than 15 people (including the driver).In addition to the power unit, a trailer with a Gross VehicleWeight Rating of up to 10,000 lbs. may be towed without requiringthe license to be upgraded.A Class B CDL is required for any non-exempt single vehicle witha Gross Vehicle Weight Rating of 26,001 lbs. or more. Additionally,a trailer with a Gross Vehicle Weight Rating of up to 10,000 lbs.may be towed without requiring an upgraded license.A Class A CDL is required for any non-exempt combination wherethe Gross Combined Weight Rating of the trailer is 10,001 lbs. ormore.These laws are a bit screwy, so let's give it a breakdown...Single vehicle:Single vehicle with a GVWR of 0 - 26,000 lbs. = no CDL requiredunless the conditions for a Class C CDL existSingle vehicle with a GVWR of 26,001 or more lbs. = Class B CDLis not in an exempt categoryCombination vehicles:Tow unit with GVW of 26,000 lbs. or less and trail unit with GVWof 10,000 lbs. or less = No CDL required unless the conditions forthe requirement of a Class C CDL apply.Tow unit with GVW of under 26,000 lbs. or less and trail unitwith a GVW of 10,001 lbs. or more but when the Gross CombinedWeight Rating is still under 26,000 lbs. = No CDL required unlessthe conditions for the requirement of a Class C CDL apply.Tow unit with a GVW of under 26,000 lbs. and a trail unit of10,001 lbs. or more for a Gross Combined Weight Rating of 26,001lbs. or more = Class A CDL required if the vehicle is of anon-exempt category.Tow unit with a GVW of 26,001 lbs. or more and a trail unit witha GVW of 10,000 lbs. or less = Class B CDL required if the vehicleis of a non-exempt category.Tow unit with a GVW of 26,001 lbs. or more and a trail unit witha GVW or 10,001 lbs. or more = Class A CDL required if the vehicleis of a non-exempt category.Feel free to PM me if you have any questions.