Here is my version. Someplace and often multiple places on the trailer will be a sticker. It will list weights/tire pressures,and sometimes other figures.
Look for GVW (GROSS VEHICLE WEIGHT), Tongue weight will be 10 to 15% of that figure.
When looking at trucks,look on the drivers side door jamb. there will be a sticker listing tire sizes,pressures and weights.
The figure you want to pay attention to is the one associated with the phrase,Weight of passengers and cargo must not exceed.
Deduct from that figure everything that was not on the truck at final assembly. deduct for everything ,your dog your cooler your kids the McNugget under the seat and the hitch. the remainder is the amount you can place on the tongue.
Very rough rule of thumb is that a 7 or 8k trailer is max for a half ton.
For everybody who is waiting to pounce, yes some halfs are more capable and some are less.
Automatic admonishments to buy a 1 ton are just plain stupid!