When drinking the night before driving:
- men should consume no more than 10 units, women no more than 7. (This assumes that no alcohol is consumed after 11.30 pm, and that driving does not take place before 8 am the following morning)
This applies to people of average weight (around 12-13 st for men, 9-10 st for women). If you are particularly small, these figures should be reduced accordingly. But if you are particularly big, it is no guarantee that they can be increased. The figures are lower for women not only because they are usually lighter than men, but also because their metabolism is different.
http://www.80mg.org.uk/guide.html