Ask five different cafes how much caffeine is in a flat white and you'll get five different answers.
The honest reason: it depends on the bean, the roast, the shot volume, and how the barista pulls it. A single espresso shot generally lands somewhere around 60–80mg of caffeine, though it varies more than most people expect between cafes — even between baristas at the same cafe.
That inconsistency makes it hard to know exactly how much you're having on a given day, especially if you're trying to manage your intake or keep it consistent.
It's part of why we like gum as a format — each piece of Neuchu has a fixed 50mg of natural caffeine, so you know exactly what you're getting every time, no barista variation involved. You can find it here.