Kerbweight - Gross weight = Load weight
That is a guide because if you have extras added such as aircon, ply lining, etc it will add to the kerb weight before you start adding your system, tools, roof rack etc..
Check out
www.whatvan.co.uk go through the search function and it will tell yothe vehicles to look at at their load weight.
To be totally sure or you think you will be close to the max then take it to a weighbridge.
Regards
Mr H