Does light roast have more caffeine?

It depends on how you measure, and the reason is mostly about measuring, not chemistry. Caffeine survives roasting almost intact; it does not “burn off.” So the headline is: per gram the roasts are nearly identical (dark is fractionally higher), per scoop light roast wins, the gap is tiny either way, and how you scoop your beans matters more than the roast level itself.

Why people think it is more

The myth that light roast has way more caffeine comes from mixing up two ways of measuring.

• By weight (grams): dark roast has a slight edge. Roasting drives off some moisture and mass, so darker beans weigh a touch less per bean, which makes their caffeine concentration per gram fractionally higher. Confusingly, that pushes dark slightly up on a per-gram basis. In practice the two are within a hair of each other.
• By scoop (volume): here light roast clearly wins. Light-roast beans are denser because they spent less time expanding in the roaster, so a scoop of light beans contains more beans, and therefore more caffeine, than the same scoop of puffed-up dark beans.

So if you measure by the scoop, switching from dark to light can give you a noticeable caffeine bump, not because light beans are caffeine bombs, but because you are quietly using more coffee. The mirror-image question is answered in is-dark-roast-stronger.

What this means in your cup

1. Weigh your coffee if caffeine consistency matters to you. A scale removes the density trick entirely. Once you weigh, the roast difference shrinks to almost nothing.
2. Want more caffeine? Use more coffee. Dose is the real lever, not roast colour.
3. Choose roast for flavour, not buzz. Light roasts taste brighter and fruitier, darker roasts taste bolder and more roasty. See roast-levels-explained.

For the full story on how caffeine behaves and how little roasting changes it, see caffeine-101 and the term caffeine.