I am looking at purchasing a used G20 van. We have a 91 g20,it is a 3/4 ton, that just can't do the hauling anymore and would like to replace it. I sent an email to a guy about his van for sale to inquire if it was a 3/4 ton because I was under the impression it could also be a 1/2 ton. Could someone clarify this for me, are g20 van's 1/2 or 3/4 or either? Also, if it could be either could you tell me how to find out which one it is if the owner doesn't know. Thank you for any help.

G10 is a 1/2 ton, G20 is 3/4 ton and G30 is a 1 ton van. Also the GMC Vandura vans are 1500- 1/2 ton, 2500 - 3/4 ton and 3500 - 1 ton.

Welcome to AF
As said G is van and a 20 is 3/4 ton.
But.
Get the vin no.
And break it down. Or post back VIN first 10 digits of vin.