Plain, nonfat Greek yogurt contains 59 calories per 100 grams, according to data from the U.S. Department of Agriculture. As such, a 170-gram, single serving of Greek yogurt has 100 calories. Traditional, plain, low-fat yogurt has a slightly higher caloric content, according to the USDA. Per 100 grams, this form of yogurt contains 63 calories; a 170-gram serving of traditional yogurt has 107 calories.