Coffee Science · No. 04
The Caffeine Ledger
"Dark roast has way less caffeine" is one of the most repeated coffee claims online — and it's misleading. Caffeine barely changes with roast level by weight. What actually changes is density — which matters enormously if you measure coffee with a scoop instead of a scale.
The myth, demonstrated
Same underlying math, two measurement modes. Watch what happens to the bars when you switch from weighing to scooping.
Your cup, estimated
Species matters far more than roast — robusta runs roughly double arabica's caffeine content by weight.
Slide toward Robusta if you're using a blend — many "high caffeine" or budget commercial blends include a meaningful robusta percentage.
E.g. a French press dose split across 2 cups — mg per serving divides accordingly.
How this is calculated
Base caffeine by weight: Arabica ≈1.3% of roasted weight, Robusta ≈2.4% — blended linearly by the species slider.
Roast adjustment (by weight): a small ±3% swing across light→dark — genuinely minor, and published sources don't even agree on its direction, so treat it as noise rather than a real lever.
Roast adjustment (by scoop): density factors of roughly 1.12× (light), 1.00× (medium reference), 0.85× (dark) — darker roasts lose more mass and expand more, so a scoop simply holds less material. This is the actual mechanism behind the myth.
Brew method: mostly changes total caffeine through typical dose/ratio conventions, not extraction efficiency — caffeine extracts fast and early in nearly every method, so we apply only a small efficiency adjustment (drip/pour-over 99%, French press 97%, espresso 96%, cold brew 93%, decaf process removes ~97% of original caffeine before roasting).
Estimated caffeine
Live, updates as you adjust
Put the lesson into practice
The single biggest takeaway from this tool: weigh, don't scoop, if you actually care about consistent caffeine. Replace the placeholder links with your own affiliate links and verified current products before publishing.
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