To make one gallon of red wine, you will need about 8 pounds of grapes. This assumes that you are using a standard sized bottle, which is 750mL. One pound of grapes will yield about 750mL of wine. 8 pounds of grapes will yield you about one gallon of wine.
Obviously, the actual amount of grapes you'll need might vary depending on the type of grapes you're using. https://islamhood.org/?p=779 For instance, concord grapes tend to have a greater sugar content than other ranges, so you may need less concord grapes to make a gallon of wine than you would of other grapes.
https://bikramyogauk.net/?p=573 The size of the grape also matters. Bigger grapes will yield more juice than smaller sized grapes, so you might need more small grapes to make a gallon of red wine than you would of large grapes. The bottom line is that it takes about 8 pounds of grapes to make one gallon of white wine.