system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do 20fl oz bottles of Diet Sierra Mist Cranberry Splash have 10 calories while 2L bottles and cans have 0?
gpt
Nutrition facts are based on serving sizes. Servings with fewer than five calories can be labeled as having zero calories. Servings with fewer than 50 calories may be rounded to the nearest 5 calories. Servings with over 50 calories may be rounded to the nearest 10 calories. 

For your question specifically, the drink contains just a few calories and the serving sizes are different for the different containers, which leads to differences in rounding. The serving size for the 20 fl oz. bottle is larger than the other two bottles and when the calories are rounded to the nearest 5 calories, you get 10. The other two serving sizes have fewer than five calories, so they can be labeled as having zero calories.