Mountain Dew has more caffeine than Diet Coke: 54mg vs 46mg in the same 12 oz can. That is a 8mg gap, and since the cans match, the per-serving number is the whole story.
Diet Coke vs Mountain Dew: the numbers
| Diet Coke | Mountain Dew | |
|---|---|---|
| Caffeine per serving | 46mg per 12 oz can | 54mg per 12 oz can |
| Caffeine per fl oz | 3.8mg | 4.5mg |
| Servings to reach 400mg (FDA context) | 8.7 | 7.4 |
Sources: Diet Coke's figure is verified in our Diet Coke caffeine guide against Caffeine Informer (source); Mountain Dew's figure is verified in our Mountain Dew guide against Caffeine Informer (source).
Which one should you pick?
Pick Diet Coke when you want the lighter dose or a slower ramp, and Mountain Dew 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 Coke: the full caffeine guide
- Mountain Dew: the full caffeine guide
- The verified caffeine database
- Every drink compared: the comparisons index
FAQ
Does Diet Coke or Mountain Dew have more caffeine? Mountain Dew: 54mg per 12 oz can versus 46mg per 12 oz can for Diet Coke.
Which is stronger per ounce? Mountain Dew, at about 4.5mg 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.