the police will look at 'all up weight' thats van plus all contents, EVERYTHING!!
best thing to do is get weighed,
otherwise you need to take 'all up weight' subtract wieght of van , thats vans 'wet weight' (with oil, coolent, fuel ect.) then left over will be weight you can put on van rember to include you and passengers,
trouble with that method you need to know weight of every item on the van and add up.
much easier get weighed and look where you are from 'all up weight'