Red Bull has more caffeine than Diet Coke on both counts: 80mg per 8.4 oz can against 46mg per 12 oz can, and about 10mg per fluid ounce against 4. The serving sizes differ, so the table below shows both ways of counting.
These are different categories of drink, which changes how the caffeine arrives. Energy drinks and sodas list an exact number because caffeine is a measured additive; brewed drinks vary with the beans and the brew, so their figures are compiled averages. The numbers here are the standard published values for each.
Red Bull vs Diet Coke: the numbers
| Red Bull | Diet Coke | |
|---|---|---|
| Caffeine per serving | 80mg per 8.4 oz can | 46mg per 12 oz can |
| Caffeine per fl oz | 9.5mg | 3.8mg |
| Servings to reach 400mg (FDA context) | 5.0 | 8.7 |
Sources: Red Bull's figure is verified in our Red Bull caffeine guide against Red Bull label / Caffeine Informer (source); Diet Coke's figure is verified in our Diet Coke guide against Caffeine Informer (source).
Which one should you pick?
Pick Diet Coke when you want the lighter dose or a slower ramp, and Red Bull 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
- Red Bull: the full caffeine guide
- Diet Coke: the full caffeine guide
- The verified caffeine database
- Every drink compared: the comparisons index
FAQ
Does Red Bull or Diet Coke have more caffeine? Red Bull: 80mg per 8.4 oz can versus 46mg per 12 oz can for Diet Coke.
Which is stronger per ounce? Red Bull, at about 9.5mg per fluid ounce versus 3.8mg for Diet Coke.
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.