Tea comes in a few different varieties, including black, green, oolong and white teas. All these types are prepared by steeping tea leaves in water, and all have the same amount of calories. While plain, freshly steeped tea is low in calories, adding milk or sugar can raise the calorie count significantly.
An 8-oz. cup of tea served without anything added to it contains 2 calories. Adding 1 tbsp. sugar adds 49 calories, while 1 tsp. provides about 16 calories. One lump of sugar is usually about 1 tsp. Skim milk adds 5 calories per tbsp.; the same amount of whole milk has about 9 calories.
In 8 oz. of black tea, there are between 40 and 120 mg of caffeine, according to MayoClinic.com. A 6-oz. cup of premium green tea has 26 mg of caffeine. Caffeine may be beneficial when consumed in amounts less than 500 mg per day.
The low calorie count in tea makes it an ideal drink for dieters, as long as you don't add a lot of milk or sugar. Tea may also increase weight loss, although this requires further study to confirm the preliminary research indicating a possible effect, according to Medline Plus.