Arms gives you a choice of:
Armoured Carriage - 3-4 inside with baggage, driver outside.
Covered carriage - 2 benches so probably 4-6 inside plus driver.
Noble Carriage - no numbers given but probably close to the 3-4 of the armoured version.
Large cart - 'several' passengers or heavy loads.
Ox cart - 'a decent amount of weight and a passenger or two'.
What exactly do you want to carry?
Just creating a wagon train for an adventure. The adventurers are part of a contingent of guards escorting the merchant train to a smaller town. The goods are to be shipped to warmer, wealthier climes in the south of my game world.
Players being what they are, I figured an overall idea of how much a wagon can carry would help me prepare what the entire shipment could potentially contain, in case they snoop ...