BAC chart: blood alcohol by weight and drinks

How the chart was made

Every cell comes from the same tested module that runs the BAC calculator. One drink in the first table is a 0.33 l bottle of 5 % beer, which holds 13.0 g of pure alcohol — close to a US standard drink of 14 g. Body weight runs down the side, the number of drinks across the top. The figure is the reading straight after the drinks, with no time for elimination: the worst case of that row and column.

The formula is Widmark's, from 1932: grams of alcohol divided by body weight times a distribution factor. The factor is 0.68 for men and 0.55 for women on average, because alcohol spreads through body water and women on average carry a smaller share of water for their mass. That single difference is why the women's table runs noticeably higher than the men's for the same glasses.

Values are in per mille (grams per litre of blood), the unit used across Europe. To read them as US % BAC, move the decimal point one place to the left: 0.80 ‰ is 0.08 %, the US legal limit; 0.50 ‰ is 0.05 %, the limit in Utah, Australia and most of Europe.

Men: 0.33 l beer at 5 %

Women: 0.33 l beer at 5 %

Women: 150 ml glass of wine at 12 %

A 150 ml glass of 12 % wine holds 14.2 g, a little more than the bottle of beer above. Many bars pour 175 ml or more, in which case add another sixth to every figure.

Reading the chart honestly

Take one row: an 80 kg man who drinks four bottles of beer in quick succession reaches about 0.96 ‰ on this model, which is 0.096 % in US units. A 60 kg woman who drinks three 150 ml glasses of wine reaches about 1.29 ‰. Those are the numbers an average body produces. Your body is not average in at least three ways that matter.

• Your elimination rate. The chart assumes nothing has been cleared yet. In reality you clear roughly 0.15 ‰ an hour from the moment alcohol reaches your blood, but the real rate between people runs from about 0.10 to 0.20. Over a four-hour evening that difference alone is worth 0.4 ‰.
• Your stomach. Drinking on an empty stomach lets alcohol reach the blood within half an hour or so. After a meal absorption can be spread over two hours or more, which lowers the peak. The total amount you have to clear is the same either way.
• Your distribution factor. 0.68 and 0.55 are averages across large groups. A lean, muscular man may sit above 0.75; a man with more body fat may sit below 0.6. If you give the calculator your height and age it works out a factor from the Watson body-water equations instead, which is closer — but it is still a model.

There is also the drink itself. Craft beers at 6 to 8 %, generous pours of wine and doubles of spirits are the norm in many places, and each of them moves you a column or two to the right without your noticing. The standard drink sizes page shows what each common glass really holds.

Why there is no "safe" column

People look at a chart like this to find the column that keeps them under a limit. That is exactly the use it cannot serve. Look at how close the numbers sit together: between two and three drinks the reading jumps by about a third, and the gap between a heavy and a light person of the same sex is larger still. A table that is right on average is wrong for most of the people reading it, by an amount that matters at a limit of 0.5 ‰ or 0.2 ‰.

The law in most countries does not care how you felt either. In Germany, Norway, Poland, Sweden, Finland and elsewhere the offence is the number itself, measured in blood or breath. Several countries go further and set zero for new drivers, for drivers under 21 and for anyone driving for a living — you can see which on the legal limits page. For them every column of this chart is over the limit from the first glass.

The only reading that is safe for driving is 0.00. If you have been drinking, do not drive — however the chart looks.

Peaks fall slowly

A chart of peaks hides the other half of the story: how long the number takes to come down. Because the liver works at a nearly fixed rate, the hours you need are the peak divided by about 0.15. A 70 kg man who drinks six half-litres of 5 % beer peaks near 2.49 ‰ and needs around 16:35–24:52 hours and minutes to reach zero. Nine hours after the first beer he is still at about 1.14 ‰. The elimination calculator draws that curve for your own drinks.

Using the calculator instead of the chart

A chart has to pick one drink, one sex and no time. The calculator lets you mix drinks, set the time since the first one, compare with the limit of your own country and see the curve over the following hours. It runs entirely in your browser; nothing you type is sent anywhere.

Where the figures come from

The density of ethanol is 0.789 g/ml at 20 °C. The distribution factors are the forensic averages published by Widmark and later by Seidl, Jensen and Alt in the International Journal of Legal Medicine (2000). The elimination rate of 0.15 ‰ per hour is the figure German and Nordic road-safety authorities use for an average adult. The About & method page lists the full method; every number in this post was printed by the same code the calculator runs, not typed by hand.