How many oranges does it take to make 1 gallon of pulp-free orange juice?

I guess it depends how big the oranges were ;-)

About 48. I just used calories to figure that out.

1760 calories for the gallon of juice. 37 calories per average orange.

16 cups x 8oz = 128 oz. = 1 gallon. Squeeze an 8 oz cup and see how many oranges you use. Then do the math. @juicyful is right about an average orange being a Platonic ideal. A bad year for juice oranges, I might add - they are less juicy than during other years. And home-squeezed juice has pulp so that complicates the calculation. (BTW, pulp is good for you - vitamins, minerals, fiber, more juice.)