"That's about one drink for a woman weighing 120 pounds, two for a 160-pound man. A "drink" means 12 ounces of beer, four ounces of wine"
I don't claim to be the world's foremost expert, but I immediately recognized that something important was omitted here. The missing ingredient is time. It takes time to drink, and BAC is basically a math problem between the amount of ethanol, body mass, and time. Basically, your body can't metabolize the alcohol in one standard drink (about a half ounce of pure ethanol) every hour, so if you consume a drink every hour over a period of time, your BAC slowly starts to build up. If you drink faster than one per hour, the concentration of alcohol builds up more quickly. It has nothing to do with tolerance, it's just math.
If the 160 lb. man drank two 12 oz. standard American beers evenly during his first hour of drinking, he would be at about .025% to .035% at the end of that hour--not .05%. It is however, true that the third beer in hour one might put him over .05% at the end of an hour--it would be close. If he drank four in hour one, he'd be getting perilously close to the current legal limit of .08%, as he would with six in three hours. Throttle back to five Buds during a three hour televised football game, though, and he is still comfortably below .08%. Since he has slowed his consumption, his liver is dealing a bit more effectively with his mouth, though still not at equilibrium.
My favorite online blood alcohol calculator is the Drink Wheel, from Intoximeters, Inc.--the company that manufactured the gas chromatographs I was trained to use a long time ago. The flame ionization detector and the Poropak Q column are still on the tip of my 37 degree Celsius tongue, 38 years later. It's called the drink wheel because long before the PC and decades before the Internet, the drink wheel was a circular contraption made of two discs of card stock that you could rotate around to select weight, beverage, and time to produce an estimate. Sure wish I had saved one of those gizmos. We used to hand them out right and left.
It is, however, only an estimate. Govern yourself accordingly, and err on the side of caution.