I don't know what happened, but it seems you cannot change the display "total weight of a swap" to grams. I tried to log out, put it to 'ounce' than back to 'grams' but nothing. Is this a bug? Or is something wrong on my side?
I mean it is not critical, a google search will get the value in grams.
The unit for the total weight of swap is based only on the country of the user. People in the United States see the weight in ounces, while people in other countries see the weight in grams.
Just to better understand your need:
Do postal services in the US happen to have price lists in grams?
If the price lists are in ounces, why do you need the weight in grams?