Diet Pepsi has more caffeine than Barq's root beer: 35mg vs 22mg in the same 12 oz can. That is a 13mg gap, and since the cans match, the per-serving number is the whole story.
Diet Pepsi vs Barq's root beer: the numbers
| Diet Pepsi | Barq's root beer | |
|---|---|---|
| Caffeine per serving | 35mg per 12 oz can | 22mg per 12 oz can |
| Caffeine per fl oz | 2.9mg | 1.8mg |
| Servings to reach 400mg (FDA context) | 11.4 | 18.2 |
Sources: Diet Pepsi's figure is verified in our Diet Pepsi caffeine guide against Caffeine Informer (source); Barq's root beer's figure is verified in our Barq's root beer guide against Coca-Cola brand data (source).
Which one should you pick?
Pick Barq's root beer when you want the lighter dose or a slower ramp, and Diet Pepsi when you actually need the bigger hit and know your tolerance. If you are stacking either with other caffeinated drinks through the day, run the math against the 400mg reference rather than guessing.
For context, the FDA cites 400mg of caffeine a day as an amount generally not associated with negative effects in healthy adults. Tolerance and health vary, so treat these numbers as information, not advice.
Related reading
- Diet Pepsi: the full caffeine guide
- Barq's root beer: the full caffeine guide
- The verified caffeine database
FAQ
Does Diet Pepsi or Barq's root beer have more caffeine? Diet Pepsi: 35mg per 12 oz can versus 22mg per 12 oz can for Barq's root beer.
Which is stronger per ounce? Diet Pepsi, at about 2.9mg per fluid ounce versus 1.8mg for Barq's root beer.
Comparing caffeine? The caffeine comparison tool puts hundreds of drinks side by side, and the caffeine curfew calculator can check your cutoff time for tonight.