Monster has more caffeine than Diet Pepsi on both counts: 160mg per 16 oz can against 35mg per 12 oz can, and about 10mg 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.
Monster vs Diet Pepsi: the numbers
| Monster | Diet Pepsi | |
|---|---|---|
| Caffeine per serving | 160mg per 16 oz can | 35mg per 12 oz can |
| Caffeine per fl oz | 10.0mg | 2.9mg |
| Servings to reach 400mg (FDA context) | 2.5 | 11.4 |
Sources: Monster's figure is verified in our Monster caffeine guide against Caffeine Informer (source); Diet Pepsi's figure is verified in our Diet Pepsi guide against Caffeine Informer (source).
The concentration gap is the striking part: Monster packs roughly 3 times the caffeine per ounce. Sipping speed matters at that density; a 16 oz can finished in minutes hits differently than the same milligrams spread over a slow cup.
Which one should you pick?
Pick Diet Pepsi when you want the lighter dose or a slower ramp, and Monster 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
FAQ
Does Monster or Diet Pepsi have more caffeine? Monster: 160mg per 16 oz can versus 35mg per 12 oz can for Diet Pepsi.
Which is stronger per ounce? Monster, at about 10.0mg per fluid ounce versus 2.9mg for Diet Pepsi.
Barista Life runs on coffee people. Browse the Barista Life shop to support the site.