The number of lemons you will need to make 3/4 cup of lemon juice depends on the size and juiciness of the lemons. On average, one lemon yields about 1/4 to 1/3 cup of juice, so you will need approximately 2 to 3 lemons to make 3/4 cup of lemon juice. It's always best to have a few extra lemons on hand just in case you need more juice.