Diet Coke vs Pepsi Zero Sugar: caffeine compared
Diet Coke (12 oz) has 46 mg of caffeine, 8 mg more than Pepsi Zero Sugar (12 oz, 38 mg) — 1.2× as much per serving. Per fluid ounce, Diet Coke is the stronger drink: 3.8 mg/oz versus 3.2 mg/oz.
| Diet Coke | Pepsi Zero Sugar | |
|---|---|---|
| Serving | 12 oz | 12 oz |
| Caffeine per serving | 46 mg | 38 mg |
| Per fl oz | 3.8 mg | 3.2 mg |
| Share of 400 mg/day | 12% | 10% |
| Servings to reach 400 mg | 8.7 | 10.5 |
| Hours until under 50 mg | already under | already under |
| Last one for an 11 PM bedtime · standard (50 mg) | 11:00 PM | 11:00 PM |
| Last one for an 11 PM bedtime · sensitive (25 mg) | 6:36 PM | 7:59 PM |
| Share of the 200 mg pregnancy limit | 23% | 19% |
One serving of each, over 16 hours
Common questions
Which has more caffeine, Diet Coke or Pepsi Zero Sugar?
Diet Coke (12 oz) has about 46 mg versus 38 mg in Pepsi Zero Sugar (12 oz): 8 mg more, or 1.2× as much.
Which is stronger per ounce, Diet Coke or Pepsi Zero Sugar?
Diet Coke: about 3.8 mg per fl oz versus 3.2 mg for Pepsi Zero Sugar. Serving size decides the total you actually drink.
How many Pepsi Zero Sugar servings equal one Diet Coke?
About 1.2 servings of Pepsi Zero Sugar (12 oz) match the caffeine in one Diet Coke (12 oz).
When should I stop drinking Diet Coke or Pepsi Zero Sugar before bed?
For an 11 PM bedtime with a 50 mg limit and a 5-hour half-life: last Diet Coke by 11:00 PM, last Pepsi Zero Sugar by 11:00 PM. Half-life varies from about 1.5 to 9.5 hours between people.
Method
Caffeine per labeled serving, from the same drink table every calculator here uses (FDA/USDA reference amounts and manufacturer labels; see caffeine content of every drink). Brewed drinks vary batch to batch, so read these as typical values. Decay uses a 5-hour average half-life with a 45-minute absorption ramp; cutoff = bedtime − 5 h × log₂(dose ÷ limit). Percentages use the FDA's 400 mg/day figure for healthy adults and the 200 mg/day limit ACOG gives for pregnancy.
Source — Diet Coke: Coca-Cola — What is caffeine? (FAQ), checked 2026-10-13.
Source — Pepsi Zero Sugar: PepsiCo Product Facts — Pepsi Zero Sugar 12 fl oz, checked 2026-10-13.