The only safe limit of alcohol to have in your blood and drive is zero!
It is not advisable to even have one drink and drive as alcohol impairs your judgement and lessens your reflexes. The official amount of alcohol is 35 microgrammes per 100ml of breath reading, this cannot be translated into an exact amount of units as it depends on many factors, height and weight, the time when last drink was consumed etc, so the best advice is not to drink at all or to order a taxi.
