There is about 100 mg of caffeine in a 1.5oz shot of espresso, and about 130 mg of caffeine in an 8oz cup of coffee.
8/1.5 = 5.33
130/5.33 = 24.39
1.5oz of regular coffee has about 24.5 mg of caffeine.
Espresso has about 4 times as much caffeine per volume.
If you drink the stuff like I do...