Every state prohibits drunk driving. Every state also acknowledges that it is legal to drink alcohol and then drive if the alcohol consumed does not impair one’s abilities.
The amount of alcohol that a person can drink in an evening and be safely under the legal limit varies from person to person. The main factors of weight, number of drinks, size of the drink, concentration (proof) of the alcohol, gender, and time of drinking all affect the outcome. In the 1930’s a Swedish scientist named Erik Widmark came up with a formula to calculate blood alcohol concentration (BAC) based on these factors. Using Widmark’s formula, it is possible to estimate BAC. In these calculations, there is a rough equivalence between a 12 oz. beer, and 6 oz. glass of wine, and a mixed drink containing 1.5 oz. of alcohol.
A woman will have a higher BAC than a man of the same weight because alcohol is more concentrated in the cells of a female. Since many women weigh less than many men, this difference is exaggerated with most people.
Many people have heard things from their friends that are easily disproven. For example, some people say that one drink an hour is a safe level. This is untrue because most humans cannot metabolize the amount of alcohol contained within a drink in one hour. A drink can easily add as much as 0.025 to the person’s BAC. Yet, the average drink Widmark’s formula assumes that for every hour since the drinking has begun, the body will eliminate only 0.015.
Something else to consider is many drinks with liquor in them have much more than 1.5 oz. of alcohol. Drinks such as martinis, long island iced teas, manhattans and others have the alcohol equivalent of 3-4 drinks in a single serving.
Others think that if they stop drinking for an hour or so before heading home their BAC will go down sufficiently to permit driving. This doesn’t work either using the elimination rate above of 0.015 per hour.
Using an average weight of 170 lbs. for a male and 130 for a female, according to Widmark’s formula, for a male with no prior DUI arrests the maximum safe number of standard drinks with 1.5 oz. of alcohol, a 6 ounce glass of wine, or 12 oz. beers is 3, the maximum for a female weighing at least 130 lbs. over 3 hours is 2. This recommendation is based on 3 hours from the first drink to driving. Maximum amounts for lighter individuals can be lower. For males and females, Widmark predicts a test result of 0.03-0.04.
For anyone who has previously been arrested for DUI, the maximum number of drinks before attempting to drive home should be zero. After all, if you have been through this once, you don’t want to even be suspected of drunk driving.