“Strong” means two different things, and they point in opposite directions here.
Concentration
Espresso is far more concentrated.
Espresso — 8 to 12% total dissolved solids. Filter — 1.15 to 1.45%.
Roughly eight times as concentrated. That is what makes it taste intense.
Caffeine per serving
Usually less than a mug of filter.
Single espresso (7–9 g of coffee) — 60 to 80 mg. Mug of filter (15 g of coffee, 250 ml / 8.5 oz) — 90 to 140 mg.
Because caffeine comes from the coffee, not the water, the dose is what matters. A single espresso uses half the coffee a mug of filter does.
Extraction yield
Interestingly, similar. Both aim for 18 to 22% of the coffee dissolving. Espresso gets there in 25 seconds under pressure; filter takes three minutes by gravity.
What espresso actually is
A method for producing a concentrated beverage quickly, not a stronger one. Concentration is why it works with milk — a filter coffee cannot carry 130 ml of milk.
The practical answer
If you want more caffeine, drink a larger volume of coffee, not a more concentrated one.
If you want more intensity in a small cup, that is espresso.
Last reviewed 30 October 2026