You'll need to find the sticker on the van's driver's side doorjamb or the owner's manual to get the *GVWR* (Gross Vehicle Weight Rating). That's the maximum weight the van can be, including its cargo. The *curb weight* (weight of the vehicle without cargo, passengers, or fuel) is usually lower and harder to find without consulting a specific model's specifications from a resource like a repair manual or a vehicle database.
Expect the curb weight to range from roughly 3,000 to 5,000 lbs (1.5 to 2.5 tons) depending on the model and options.