The amount of grapes you will need to make a gallon of wine can vary depending on the type of grapes you are using and the desired flavor and character of the wine. As a general rule of thumb, you will need about 20-25 pounds of grapes to make a gallon of wine.
However, it is worth noting that the amount of grapes you will need can also depend on the grape variety, the ripeness of the grapes, and the specific winemaking techniques you are using. Some grapes may yield more juice than others, and you may need to adjust the amount of grapes you use accordingly.
It is also important to note that the amount of grapes you will need to make a gallon of wine is not the same as the amount of wine you will end up with. The wine making process involves the fermentation of the grape juice, which can cause some of the juice to be lost to evaporation or conversion to alcohol. As a result, you may end up with slightly less than a gallon of finished wine.