One lemon yields about 2-3 tablespoons of lemon juice.
lime juice (This is more acidic and has a different and more pronounced flavor. Substitute 3/4 cup ordinary (Persian) lime juice or 2/3 cup key lime juice for one cup lemon juice.) OR vinegar (Especially malt vinegar. Substitute ½ cup vinegar for every cup of lemon juice. Products made with vinegar tend to keep longer than those made with lemon juice.) OR crushed vitamin C tablets dissolved in water (This works well to prevent fruit from discoloring.)