Orange wine is made from grapes. Not oranges. You muppet.
jp5040 is close. The size of an orange does not predict the amount of the juice, however. The WEIGHT of the orange gives you the best answer. Always use "valencias" for best juice. A "navel" is for eating, not juicing. The valencia has a thin and not always very pretty skin, but, that does not matter because you use if for juice. You can go weigh an average size juicing orange (valencia) & multiply that by 12, then remeber, a pound's a pound the world around. Convert it. There are usually wieght & measure conversions in any cookbooks (& substitutions).
Not only does it depend on the size of the oranges, but it also depends on how much you squeeze the oranges :)