Keep to 400 mg of caffeine a day, about four mugs of filter coffee, and no more than 200 mg at once; in pregnancy keep to 200 mg a day.
The European Food Safety Authority found no safety concern for healthy adults at up to 400 mg a day or 200 mg in one dose (about 3 mg per kilogram for a 70 kg adult), and for pregnancy it gives 200 mg a day. A mug of filter coffee has about 95 mg, so 400 mg is 4.2 mugs.
The limits are for healthy adults; children and teenagers have lower ones, and medicines, heart conditions and pregnancy change what is sensible. People differ a great deal in how much they can take before feeling jittery or sleeping badly.
Estimate with the rule, then check it against the calculator that models it properly.
Open Caffeine Curve →