Starbucks London Fog carries more total caffeine per serving (40mg per 16 oz grande (40mg at every size) vs 35mg per 12 oz can), but ounce for ounce Diet Pepsi is actually the stronger drink at about 3mg per fluid ounce against 2. Which one "has more caffeine" depends on whether you measure the container or the concentration.
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.
Diet Pepsi vs Starbucks London Fog: the numbers
| Diet Pepsi | Starbucks London Fog | |
|---|---|---|
| Caffeine per serving | 35mg per 12 oz can | 40mg per 16 oz grande (40mg at every size) |
| Caffeine per fl oz | 2.9mg | 2.5mg |
| Servings to reach 400mg (FDA context) | 11.4 | 10.0 |
Sources: Diet Pepsi's figure is verified in our Diet Pepsi caffeine guide against Caffeine Informer (source); Starbucks London Fog's figure is verified in our Starbucks London Fog guide against Starbucks nutrition listing (source).
Which one should you pick?
Pick Diet Pepsi when you want the lighter dose or a slower ramp, and Starbucks London Fog 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
- Starbucks London Fog: the full caffeine guide
- The verified caffeine database
FAQ
Does Diet Pepsi or Starbucks London Fog have more caffeine? Starbucks London Fog: 40mg per 16 oz grande (40mg at every size) versus 35mg per 12 oz can for Diet Pepsi.
Which is stronger per ounce? Diet Pepsi, at about 2.9mg per fluid ounce versus 2.5mg for Starbucks London Fog.
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.