As a "rule of thumb", double the "ton" rating.

For example, my 1-ton dually is factory-claimed at 4414# in the bed.


I'd agree if you need to go 70 mph. If you're willing to drive 40 and have
good tires, I routinely haul 6000 lb. in my old 93 ford 1 ton dually. Brakes
ain't to good with this much weight.

Karl