How much caffeine is in diet Coke? November 10, 2021 By caffeinelevel How much caffeine is in diet Coke? The caffeine content is 46mg for a 12oz can of Diet Coke. Coca-Cola Zero Sugar contains a bit less at 34mg of caffeine according to Coca-Cola’s website. Which do you like better? Is there more caffeine in regular Coca-Cola? Coke’s caffeine content is actually lower at 34mg for a 12-oz can with Diet Coke caffeine content at 46mg.