@cstross I like your number:
I measured a cutaway diagram from https://thespacebucket.com/a-closer-look-at-new-glenn-its-progress/ to get a rough estimate of the length of the tanks, got a volume for a 7 meter cylinder and multiplied by density (assuming the minimum density for LNG) and get 1,600 metric tons. Add in miscellaneous (cargo, engines) and I think you're there.