How much alcohol is too much?

How much alcohol is too much, for driving or for your health?
The number of drinks consumed is a very poor measure of intoxication because of variations in physiology and individual alcohol tolerance.
Blood/Breath Alcohol Concentration (BAC) is the amount of alcohol in the bloodstream or on one’s breath. BAC is expressed as the weight of ethanol, in grams, in 100 milliliters of blood, or 210 liters of breath. BAC can be measured by breath, blood, or urine tests.
Neither BAC, nor the number of drinks consumed, are necessarily accurate indicators of the level of impairment. Tolerance to alcohol also varies from one person to another, and can be affected by such factors as genetics, adaptation to chronic alcohol use, and the synergistic effects of drugs.
In Pennsylvania, New York, and New Jersey, as in most states, you are legally intoxicated at a BAC of 0.08, no matter your age.
How blood-alcohol concentrations affect the bodyThe following chart explains how degrees of blood-alcohol concentration affect the body:
0.020-0.039 percent
No loss of coordination, slight euphoria, and loss of shyness. Relaxation, but depressant effects are not apparent.
0.040-0.059 percent
Feeling of well-being, relaxation, lower inhibitions, and sensation of warmth. Euphoria. Some minor impairment of judgment and memory, lowering of caution.
0.06-0.099 percent
Slight impairment of balance, speech, vision, reaction time, and hearing. Euphoria. Reduced judgment and self-control. Impaired reasoning and memory.
0.100-0.129 percent
Significant impairment of motor coordination and loss of good judgment. Speech may be slurred; balance, peripheral vision, reaction time, and hearing will be impaired.
0.130-0.159 percent
Gross motor impairment and lack of physical control. Blurred vision and major loss of balance. Euphoria is reducing and beginning dysphoria (a state of feeling unwell)
0.160-0.199 percent
Dysphoria predominates, nausea may appear. The drinker has the appearance of a sloppy drunk.
0.200-0.249 percent
Needs assistance in walking; total mental confusion. Dysphoria with nausea and vomiting; possible blackout.
0.250-0.399 percent
Alcohol poisoning. Loss of consciousness.
0.40 percent +
Onset of coma, possible death due to respiratory arrest.
The time factorTime is the only factor that lowers blood-alcohol content. Coffee, cold showers, and other regimens are all myths.
For example, a man goes to bed at 2 a.m. with a blood-alcohol content of 0.20. When he gets up at 9 a.m., his BAC is 0.095, which is legally intoxicated. If he drives to work and gets pulled over, he will be arrested for DUI. At 3 p.m., he still has a BAC of .005.
This list gives the hours since a last drink, and the number that can be subtracted from the BAC:
1 hour, subtract 0.015
2 hours, subtract 0.030
3 hours, subtract 0.045
4 hours, subtract 0.060
5 hours, subtract 0.075
6 hours, subtract 0.090
Source: University of Notre Dame: mcwell.nd.edu