English breakfast tea has more caffeine than Diet Pepsi on both counts: 47mg per 8 oz cup against 35mg per 12 oz can, and about 6mg per fluid ounce against 3. 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.
Diet Pepsi vs English breakfast tea: the numbers
| Diet Pepsi | English breakfast tea | |
|---|---|---|
| Caffeine per serving | 35mg per 12 oz can | 47mg per 8 oz cup |
| Caffeine per fl oz | 2.9mg | 5.9mg |
| Servings to reach 400mg (FDA context) | 11.4 | 8.5 |
Sources: Diet Pepsi's figure is verified in our Diet Pepsi caffeine guide against Caffeine Informer (source); English breakfast tea's figure is verified in our English breakfast tea guide against Twinings published figure (source).
Which one should you pick?
Pick Diet Pepsi when you want the lighter dose or a slower ramp, and English breakfast tea 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
- English breakfast tea: the full caffeine guide
- The verified caffeine database
FAQ
Does Diet Pepsi or English breakfast tea have more caffeine? English breakfast tea: 47mg per 8 oz cup versus 35mg per 12 oz can for Diet Pepsi.
Which is stronger per ounce? English breakfast tea, at about 5.9mg per fluid ounce versus 2.9mg for Diet Pepsi.
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.