The main active substance in coffee, as we all know, is caffeine. The ‘safe’ daily amount of coffee you can consume, therefore, is based on the amount of caffeine you can safely consume every day without health complications.
This chemical compound is safe in low compounds, but the excessive and prolonged consumption is linked to the problems with the cardiovascular system and in women may have a detrimental effect on the foetus development during pregnancy. Short-term adverse effects of high caffeine intake include disruption in the sleeping pattern, anxiety and others (according to European Food and Safety Authority ).
In 2015, European Food and Safety Authority evaluated the effects of the caffeine consumption and stated, that single doses of caffeine of up to 200 mg and daily intake of up to 400 mg present no risk for the general adult population. The recommendation for pregnant women is to consume no more than 200 mg per day. Another recommendation is not to consume more than 100 mg of coffee before the bedtime. It constitutes to around 3-5 cups of coffee per day.
Different coffee drinks have different amounts of caffeine and this depends on multiple factors, like the variety of the coffee beans, processing, brewing methods etc. It is also important to remember, that coffee is not the only source of caffeine: other drinks, e.g. cocoa, energy drinks also contribute to the daily intake of coffee.
Have a look at the diagram I’ve made (adopted from EFSA data). Bear in mind, that this is just average values for each drink and in reality, the concentrations may differ quite significantly. Also, compare different volumes (e.g. 60 ml of espresso contains more caffeine than 200 ml of cappuccino).