No need to be concerned. The kits are designed to add water up to the recommended volume (eg: 23 litres, 6 US gallons or 5 Imp gallons). Some kits are all juice and you don't add any water.
All this is very confusing. If you use metric it is a LOT easier. The full size kits generally...
No need for the complicated math. By definition 1 US fluid gallon is 128 fluid ounces. The weight is irrelevant. You are mixing up fluid ounces and 'weight' ounces. They are not the same. The weight of 1 US gallon is indeed approximately 133.7 ounces but it is still 128 fluid ounces.
