Subtract the hitch loads from the Cargo Weight Rating (CWR). CWR is the maximum weight of the load the vehicle can carry. It does not include the weight of the people inside, but you can figure about 150 lbs. (68 kg) for each passenger. The total cargo load must not be more than the vehicles CWR.
Weigh the vehicle with the trailer attached, so the GVWR or GAWR are not exceeded. If using a weight-distributing hitch, weigh the vehicle without the spring bars in place.
The best performance is obtained by correctly spreading out the weight of the load and choosing the correct hitch and trailer brakes.
For more information see Towing a Trailer.