Caffeine in drinks
How much caffeine is in Diet cola?
Data checked against the source on 2026-10-03 by Oleksii Y.
One 12 fl oz can (355 g) of Diet cola has 42.6 mg of caffeine, according to USDA Agricultural Research Service, FoodData Central (SR Legacy).
How Diet cola compares
- Strength: 12 mg per 100 ml.
- One 12 fl oz can (355 g) has as much caffeine as about half a cup of brewed coffee, which has 94.8 mg per 8 fl oz cup.
- Of the 22 other sodas in our soda chart, 3 have more caffeine per serving and 19 have less.
How much will be left at bedtime?
1 × 12 fl oz can (355 g) of Diet cola
Left at 11:00 PM (8 h later), average metabolism
≈ 14 mg
Range 7–22 mg (fast to slow metabolism)
43 mg is already at or under the 50 mg this tool aims to have left at bedtime.
What sleep studies found near this dose
- Gardiner et al. 2025 (randomized trial): In 23 healthy young men, 100 mg taken 12, 8 or 4 hours before bed had no significant effect on measured or self-rated sleep.
- Gardiner et al. 2023 (meta-analysis): To avoid losing sleep time, the authors suggest a coffee (107 mg per 250 ml) at least 8.8 hours before bed.
Estimate from a simple model: half-life of 3, 5 or 8 hours, 50 mg bedtime target. How we calculate
How long does Diet cola stay in your system?
Our model halves caffeine every 5 hours for average metabolism, and every 3 or 8 hours for fast or slow metabolism. From one 12 fl oz can (355 g) of Diet cola (43 mg), about 22 mg is still in your body 5 hours later and about 11 mg after 10 hours. If you clear caffeine slowly (an 8-hour half-life), about 18 mg is left after 10 hours.
Estimated caffeine left at 11:00 PM from one 12 fl oz can (355 g) (43 mg), using a half-life of 5 hours for average metabolism and 3 to 8 hours for the range. How we calculate
| Had at | Left at bedtime (average) | Range |
|---|---|---|
| 8:00 AM (15 h before bed) | ≈ 5 mg | 1–12 mg |
| 12:00 PM (11 h before bed) | ≈ 9 mg | 3–17 mg |
| 3:00 PM (8 h before bed) | ≈ 14 mg | 7–22 mg |
| 6:00 PM (5 h before bed) | ≈ 22 mg | 14–28 mg |
How many fit in a day?
Reference amounts are for caffeine from all sources combined. Counted at the upper end of the stated amount, one serving at a time:
- Up to 400 mg a day for most healthy adults (FDA, EFSA): about 9 servings.
- Up to 200 mg at one time for healthy adults (EFSA): about 4 servings in one go.
- Up to 200 mg a day in pregnancy (EFSA, NHS): about 4 servings.
These are reference amounts for groups of people, not a personal limit. Some people feel jittery or sleep worse on much less. See the cutoff calculator for timing.
Good to know
Health Canada lists 39 to 50 mg for a 355 ml can of diet cola, against 36 to 46 mg for regular cola.
How the serving amount was worked out: USDA lists 12 mg per 100 g for diet cola or pepper-type soda with caffeine (7 analysed samples, min 3, max 20); 355 g × 0.12 = 42.6 mg. The sample min and max give 10.7 to 71.0 mg per can.
Diet cola vs other generic cola drinks
- Cola: Diet cola has more caffeine than cola per 12 fl oz can (355 g): 42.6 mg vs 33.3 mg.
Common questions
How much caffeine is in Diet cola?
USDA Agricultural Research Service, FoodData Central (SR Legacy) gives 42.6 mg of caffeine per 12 fl oz can (355 g).
How many Diet cola servings can I have in a day?
The FDA and EFSA cite up to 400 mg of caffeine a day, from all sources combined, for most healthy adults. At 42.6 mg per 12 fl oz can (355 g), that is about 9 servings if Diet cola is your only source. In pregnancy the reference is 200 mg a day.
How late can I drink Diet cola?
One serving has about 43 mg, which is at or under the 50 mg our calculator aims to have left at bedtime, so it sets no cutoff for a single serving. Several servings add up.
Does Diet cola have more caffeine than Cola?
Diet cola has more caffeine than cola per 12 fl oz can (355 g): 42.6 mg vs 33.3 mg.
How long does Diet cola stay in your system?
Of the 43 mg in one 12 fl oz can (355 g), roughly 22 mg remains after 5 hours and 11 mg after 10 hours with our average 5-hour half-life. From fast to slow metabolism, 10 hours later it is between 4 and 18 mg.
Where the number comes from
- Beverages, carbonated, low calorie, cola or pepper-type, with aspartame, contains caffeine. USDA Agricultural Research Service, FoodData Central (SR Legacy). FDC ID 175099, nutrient "Caffeine" (262): portion "1 can 12 fl oz" = 355 g. Accessed 2026-10-02. Source ↗
- Caffeine in foods. Health Canada. Table 2 "Average amounts of caffeine in food and drink", rows "Cola beverage, diet | 355 ml | 39 to 50 mg" and "Cola beverage, regular | 355 ml | 36 to 46 mg" Accessed 2026-10-02. Source ↗
Recipes and labels change. If a number here no longer matches the label, the label wins.
General information, not medical advice
If you feel unwell after caffeine — for example chest pain, a fast or irregular heartbeat that does not settle, fainting, confusion or trouble breathing — get urgent medical help. If you are pregnant or breastfeeding, under 18, take medication, or have a heart, liver or anxiety condition, high blood pressure or a sleep disorder, ask a doctor or pharmacist what amount is right for you.
Sources
- U.S. Food and Drug Administration (2024). Spilling the Beans: How Much Caffeine is Too Much? FDA Consumer Updates. fda.gov ↗
- European Food Safety Authority. Caffeine | EFSA. EFSA topic page (summary of the 2015 Scientific Opinion on the safety of caffeine). efsa.europa.eu ↗
- NHS. Foods to avoid in pregnancy. NHS. nhs.uk ↗
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