How much caffeine is in Coca-Cola Coke Zero?

A 355 ml (12 fl oz) can of Coca-Cola Coke Zero contains 34 mg of caffeine, which works out to a concentration of 9.6 mg per 100 ml. That is roughly one-third of the caffeine in a standard 240 ml cup of drip coffee (96 mg), placing it at 0.4× the coffee reference. The dose is low enough that most adults will not feel a pronounced stimulant effect from a single can, but it is not zero. At 34 mg, the caffeine is comparable to what one would get from a 240 ml cup of green tea (28 mg) or a small chocolate bar, and it is about half the amount in a single espresso shot (63 mg). Because the caffeine is dissolved in a carbonated liquid, absorption begins in the mouth and stomach, with peak plasma levels typically reached 30–60 minutes after finishing the drink.

The subjective experience depends heavily on individual tolerance. Someone who rarely consumes caffeine may notice a mild lift in alertness and a slight increase in heart rate, while a habitual coffee drinker might register no perceptible change at all. The 34 mg dose is 9% of the widely cited 400 mg daily maximum for healthy adults set by the FDA and EFSA, so a single can fits easily within a moderate intake. For context, one would need to drink roughly 12 cans of Coke Zero in a day to reach that 400 mg ceiling, though the volume of liquid and the sweeteners would likely become limiting factors long before the caffeine.

How long Coca-Cola Coke Zero stays in your system

Caffeine elimination follows first-order kinetics with a population-average half-life of 5.7 hours. For a 34 mg dose, the amount remaining in the body can be estimated as: 34 × 0.5^(hours/5.7). After 3 hours, approximately 24 mg remain; after 6 hours, 16 mg; after 9 hours, 11 mg; and after 12 hours, about 8 mg. By the 12-hour mark, the circulating caffeine has dropped to a level lower than that found in a 240 ml cup of decaffeinated coffee (which typically contains 2–5 mg). This rapid decline means that for most people, a single can consumed in the early afternoon will be largely cleared by bedtime.

If someone drinks a Coke Zero at 15:00, the model predicts that at 23:00 — eight hours later — roughly 13 mg of caffeine would still be active. That is a small amount, equivalent to about half a cup of green tea. For the majority of adults, this residual caffeine is unlikely to interfere with sleep onset or sleep quality. However, a 2013 study by Drake et al. (Journal of Clinical Sleep Medicine) demonstrated that even 400 mg of caffeine taken six hours before bed can reduce total sleep time by more than an hour, which underscores that individual sensitivity varies widely. For a person who is a slow caffeine metaboliser — whether due to genetics, liver function, or medication use — the half-life can extend to 8–10 hours, meaning that the same 15:00 Coke Zero could still leave over 20 mg in circulation at 23:00, a dose that might be sufficient to delay sleep in sensitive individuals.

The 34 mg in a single can of Coke Zero represents 9% of the FDA and EFSA daily caffeine guidance of 400 mg for healthy adults. That is a small fraction, and even four cans spread across a day (136 mg) would still leave plenty of room before hitting the limit. For a pregnant woman, however, the EFSA recommends limiting daily intake to 200 mg, so one can accounts for 17% of that ceiling — still modest, but worth tallying if other sources are present. Adolescents are advised by Health Canada to consume no more than 2.5 mg per kilogram of body weight per day; for a 50 kg teenager, that equates to 125 mg, making a single Coke Zero 27% of the daily cap. In all cases, the dose is low enough that it can be incorporated into a mindful caffeine budget without much difficulty.

When it comes to sleep, timing matters more than the absolute dose. Using the 5.7-hour half-life, a 34 mg dose consumed at 18:00 would leave about 20 mg in the body at 23:00, which is enough to occupy a significant fraction of adenosine receptors in a sensitive person. To reduce the bedtime residual below 10 mg, the last Coke Zero should ideally be finished by 11:00 on the same day — a 12-hour buffer. For most people, that level of caution is unnecessary; a can at 15:00 or even 16:00 is unlikely to cause problems. The latest-cup-before-bed tool lets one enter a usual bedtime and see a personalised cut-off time based on sensitivity level. For those who know they are slow metabolisers — a trait present in about 10–15% of the population due to CYP1A2 gene variants — an even wider margin is prudent. The safe daily limit tool can also translate the 400 mg guidance into a body-weight-adjusted number, which is especially useful for lighter individuals.

At 34 mg of caffeine per 355 ml, Coke Zero sits in the lower middle of the soda category. It contains exactly the same amount of caffeine as a regular Coca-Cola (34 mg), which surprises many consumers who assume that sugar-free versions are also stimulant-free. In fact, the zero-sugar formulation was designed to mimic the taste and mouthfeel of the original, and caffeine is part of that flavour profile. Among major cola brands, Diet Coke is noticeably higher at 46 mg, while Pepsi (38 mg) and Diet Pepsi (35 mg) are only marginally above Coke Zero. Mountain Dew, at 54 mg, delivers nearly 60% more caffeine per can, and Club-Mate, a caffeinated mate-based soda, contains 66 mg per 330 ml — almost double the Coke Zero dose. On the lower end, Barq’s Root Beer has just 22 mg, and some root beers and lemon-lime sodas are caffeine-free entirely.

Compared to coffee, the gap is substantial. A single 240 ml cup of drip coffee (96 mg) contains almost three times the caffeine of a Coke Zero. Even a single 30 ml espresso shot (63 mg) has nearly twice the dose. This means that for someone trying to reduce their caffeine intake, replacing a morning coffee with a Coke Zero cuts the stimulant load by roughly two-thirds. However, because the caffeine in soda is often consumed more casually — as a refreshment rather than a deliberate stimulant — people can easily lose track of how many milligrams they are accumulating. Two cans of Coke Zero with lunch and one in the afternoon add up to 102 mg, which is already more than a cup of coffee. The side-by-side comparison tool allows stacking multiple drinks and seeing the cumulative total in real time.

What changes the number for Coca-Cola Coke Zero

The caffeine content of Coca-Cola Coke Zero is consistent across the standard 355 ml can sold in the United States, but several factors can shift the number a consumer actually ingests. The most obvious variable is serving size: a 500 ml bottle (common in many markets) would contain proportionally more caffeine — roughly 48 mg, assuming the same concentration of 9.6 mg/100 ml. Conversely, a 222 ml mini can would deliver about 21 mg. The formulation itself, however, is designed to deliver a consistent caffeine dose per unit volume, and Coca-Cola’s quality control maintains tight tolerances. In 2017, the product was rebranded from “Coca-Cola Zero” to “Coca-Cola Zero Sugar,” but the caffeine content remained unchanged at 34 mg per 355 ml.

It is important to distinguish Coke Zero from genuinely caffeine-free products. The Coca-Cola company offers a Caffeine-Free Coca-Cola Zero Sugar variant in some regions, which contains no added caffeine and tests at 0 mg. That drink is labelled explicitly as “caffeine-free,” a term that in the United States means no caffeine has been added during manufacture. This differs from “decaffeinated,” a term reserved for beverages that originally contained caffeine but have had most of it removed — decaf coffee, for example, still carries a residual 2–5 mg per 240 ml cup. Coke Zero is neither caffeine-free nor decaffeinated; it is a caffeinated soda with a deliberately low dose. Consumers who are trying to avoid caffeine entirely should look for the words “caffeine-free” on the label, not just “Zero” or “Diet,” because both Coke Zero and Diet Coke (46 mg) contain caffeine.

Another source of variation is the fountain dispense. When Coke Zero is served from a soda fountain, the final caffeine concentration depends on the syrup-to-carbonated-water ratio, which can drift over time if the equipment is not calibrated regularly. A fountain drink might therefore deliver anywhere from 30 to 40 mg per 355 ml serving, though the target remains 34 mg. For the most accurate count, the packaged can or bottle value is the most reliable reference point. Our dataset uses the manufacturer’s published figure for the standard 355 ml can, and we update it whenever a formulation change is announced.

Where this figure comes from

The 34 mg figure for a 355 ml can of Coca-Cola Coke Zero is taken directly from the product label and the nutrition information published by The Coca-Cola Company on its official website. In the United States, the FDA requires that added caffeine be declared on the ingredient list, but it does not mandate a quantitative amount on the label unless the product makes a claim about caffeine content. Coca-Cola voluntarily discloses the caffeine content per serving, and independent laboratory testing by consumer groups has repeatedly confirmed that the actual caffeine levels in packaged sodas fall within a few milligrams of the stated value. Our dataset relies on these manufacturer-published numbers, cross-checked against the USDA FoodData Central database where available.

Published values can differ between countries because of local regulations, sweetener blends, and consumer preferences. For example, a 330 ml can of Coca-Cola sold in the UK contains 32 mg of caffeine, while the same volume in the US would contain approximately 31.5 mg (scaled from the 355 ml figure). These differences are small but real, and they explain why a visitor might see a slightly different number on a local can. We update the open caffeine dataset whenever a manufacturer announces a reformulation — as happened when Coca-Cola Zero was rebranded to Coca-Cola Zero Sugar in 2017 — and we note the date of the last verification. If a discrepancy is spotted between our figure and a current label, we encourage submission through our dataset contribution page, because the open dataset is maintained by the community and benefits from real-world verification.

Bottom line

Coca-Cola Coke Zero delivers 34 mg of caffeine per 355 ml can, a concentration of 9.6 mg per 100 ml. That is 0.4 times the caffeine in a standard 240 ml drip coffee (96 mg) and 9% of the 400 mg daily limit for healthy adults. The dose is low — comparable to a cup of green tea — and for most people it will not cause noticeable stimulation or sleep disruption when consumed in the afternoon. However, it is not caffeine-free, and the amount is identical to that in regular Coca-Cola. Anyone who needs to avoid caffeine entirely should choose a product explicitly labelled “caffeine-free,” because “Zero” refers to sugar, not stimulants. For those tracking their intake, the 34 mg can be logged alongside other sources to stay within personal and medical guidelines.