Can anyone tell me what the weight limit is for the tailgate to hold?

I have a 2013 crewcab short bed

 

They hold quite a bit of weight. Every year I buy 3 tons of wood pellets, each pallet weighs 2000lbs so I make three trips. While unloading, I stack 5 bags on the tailgate, 40lbs ea., plus the weight of myself, 250lbs and it all adds up to 450lbs +.

 

https://www.f150forum.com/f118/2016-...pacity-413901/

 

I thought they are generally 600lb. Not sure why I think that.