It all depends on the strength, the ratio, the beans. I buy my beans from a roastery close to us, drink espresso (double shot) in the morning or dilute it with water (Americano). I take standard 16g of beans for double shot. So, I feel everything that is above 3 of these per day is too much for me. So, it all depends, my cup can be different from your cup. So, how can it be compared?
Right now I'm at one cup made with 20g coffee to 300g water. So roughly 200mg caffeine. This much is the upper limit for me daily, and I get minor side effects from it, so I have to be extra cautious about dehydration, electrolytes, and diet. I have the one cup in the morning and stop drinking by 11-noon, or I drink it very slowly and my last sips are no later than 1pm.