The legal limit is 35 in Breath, 80 in blood and 107 in Urine.
But what does that mean in terms of the amount of drink?
|This is very difficult to predict as there are a large number of factors to be taken into account; amount of drink, type of drink, height, weight, what you have had to eat, how long after your last drink, etc.As a very rough guide 5 pints of normal strength lager would give a reading of 71 and 4 double vodkas would give a reading of around 49. These are very rough guides and in no way should be used as a predictor of whether you can drive. The only advice is not to have any alcohol at all if you are driving.
Wilkinsons Road traffic offences book, the ‘bible’ for drink drive and other motoring offences, provides a table of how quick the body metabolises alcohol. This is a very rough and ready guide to the likely readings.
It works on the principle that the average metabolic rate of alcohol destruction by the body is 6.5µg/100ml. So if you were twice the legal limit and had a reading of 70µg/100ml it would take over 5 ½ hours before you were under the legal limit.
This is especially important to remember when driving the following morning after a heavy drinking session the night before. It is not uncommon to see readings in excess of 100. Assuming you stopped drinking at 2:00am then you would not be under the limit until up to 10 hours later depending on what time you started to drink. Almost certainly you would be over the limit if you drive to work the next morning at 8:00.