Adding to Fonzie's link, with a 5th wheel you only need to go across CAT scales 2 times. 1 time with the combo, with the truck axles on individual sections, and the dual axles on another section. Then drop the 5th wheel in the parking lot, and weigh the truck with the axles again on individual sections. The 2 truck axles with the 5th wheel attached minus the 2 truck axles without the 5th wheel is equal to the pin weight.
Do both weigh-ins with the same tank levels, and cargo and passengers in the same positions.
You can also get accurate weights using a single section scale, but it involves more weigh-ins (front truck axle, both truck axles, total axles, just trailer axles) and more calculations.
Chap , DW Joy, and Fur Baby Sango
2006 Ford F150 Super Cab 4x4
2008 Surveyor 263