How do you know how many oranges to buy when a recipe calls for a certain amount of fresh orange juice or zest?
Oranges can greatly vary in size, so all I can do is give you general guidelines. But err on the side of buying too many: you can always eat them as is!
2 to 4 medium oranges = about 1 cup juice
2 medium oranges = 1 cup orange sections
1 orange = 4 teaspoons zest