What blood alcohol content means
Blood alcohol content (BAC), also called blood alcohol concentration, is the share of your blood that is alcohol. It is commonly written as a percentage, so 0.05% means about 0.05 grams of alcohol per 100 milliliters of blood. Some countries state the same quantity in grams per liter or milligrams per milliliter, and breath tests use their own units, so numbers from different sources cannot be compared until the unit is known. A breath analyzer estimates blood level from the alcohol in exhaled air; a blood test measures it directly. This page does neither. It calculates a theoretical figure from three inputs: how heavy you are, your sex, and how much alcohol you swallowed.
The Widmark formula, step by step
The Swedish chemist Erik Widmark described this model in the early twentieth century, and variations of it are still the standard teaching example. The version used here is:
BAC (%) = alcohol (g) Γ· (weight (kg) Γ 1000 Γ r) Γ 100 β Ξ² Γ hours
- Alcohol in grams. This is the volume of the drink multiplied by its strength and by 0.789, the density of ethanol in grams per milliliter. A 355 ml beer at 5% contains 355 Γ 0.05 Γ 0.789 β 14.0 g. The calculator treats 14 g as one standard drink. Other countries define a standard drink differently, commonly between 8 g and 14 g, so always compare grams, not glasses.
- r, the distribution ratio. Alcohol dissolves in body water, not in fat. A person with more water per kilogram of body weight dilutes the same alcohol more. This tool uses 0.68 for men and 0.55 for women, which are commonly quoted averages. Individuals vary, and body fat percentage is the main reason.
- Ξ², the elimination rate. The liver removes alcohol at a roughly steady rate. The tool assumes 0.015 percentage points per hour. Real rates differ between people and over time, so treat this as a placeholder rather than a measurement.
In plain words: divide the alcohol you took in by the mass of water-like tissue it spreads through, then subtract what the liver has removed since. Several useful facts follow directly. A lighter person gets a higher figure from the same drink. Using these averages, a woman gets a higher figure than a man of the same weight, by a factor of 0.68 Γ· 0.55, about 1.24. And because elimination proceeds at a roughly steady pace, nothing speeds it up: coffee, cold showers and fresh air may make you feel more alert but do not remove alcohol from the blood faster.
The formula also simplifies the timeline. It subtracts elimination from the moment drinking starts, while in reality the level rises as alcohol is absorbed, peaks, and then falls. That means the number it prints for the first hour or two can be lower than the real value, which is one more reason the result must not be used for safety decisions.
How much pure alcohol is in common servings
A "drink" is not a fixed amount. What matters is grams of ethanol, and the table below calculates them from volume and strength using the same density as the tool. The last column expresses each serving in the 14 g standard drinks the tool asks for.
| Serving | Volume (ml) | ABV (%) | Pure alcohol (g) | In 14 g standard drinks |
|---|---|---|---|---|
| Beer, 355 ml (12 US fl oz) at 5% | 355 | 5 | 14.0 | 1.00 |
| Beer bottle, 330 ml at 5% | 330 | 5 | 13.0 | 0.93 |
| Beer, 500 ml at 5% | 500 | 5 | 19.7 | 1.41 |
| Beer, UK pint 568 ml at 4% | 568 | 4 | 17.9 | 1.28 |
| Wine, 150 ml glass at 12% | 150 | 12 | 14.2 | 1.01 |
| Spirits, 44 ml (1.5 fl oz) at 40% | 44 | 40 | 13.9 | 0.99 |
| Large wine pour, 250 ml at 13% | 250 | 13 | 25.6 | 1.83 |
Strength varies widely within one drink type, and restaurants often pour more than the nominal amount. Check the ABV on the label, and when in doubt round the number of drinks up rather than down.
Reference estimate tables
Each cell shows the peak estimate (%) if all the alcohol were absorbed instantly, followed by the theoretical hours to reach zero at 0.015% per hour. These are outputs of the formula, not times at which any activity is safe.
Male (r = 0.68)
| Drinks | 50 kg | 60 kg | 70 kg | 80 kg | 90 kg |
|---|---|---|---|---|---|
| 1 | 0.041 / 2.7 h | 0.034 / 2.3 h | 0.029 / 2.0 h | 0.026 / 1.7 h | 0.023 / 1.5 h |
| 2 | 0.082 / 5.5 h | 0.069 / 4.6 h | 0.059 / 3.9 h | 0.051 / 3.4 h | 0.046 / 3.1 h |
| 3 | 0.124 / 8.2 h | 0.103 / 6.9 h | 0.088 / 5.9 h | 0.077 / 5.1 h | 0.069 / 4.6 h |
| 4 | 0.165 / 11.0 h | 0.137 / 9.2 h | 0.118 / 7.8 h | 0.103 / 6.9 h | 0.092 / 6.1 h |
| 5 | 0.206 / 13.7 h | 0.172 / 11.4 h | 0.147 / 9.8 h | 0.129 / 8.6 h | 0.114 / 7.6 h |
| 6 | 0.247 / 16.5 h | 0.206 / 13.7 h | 0.176 / 11.8 h | 0.154 / 10.3 h | 0.137 / 9.2 h |
Female (r = 0.55)
| Drinks | 50 kg | 60 kg | 70 kg | 80 kg | 90 kg |
|---|---|---|---|---|---|
| 1 | 0.051 / 3.4 h | 0.042 / 2.8 h | 0.036 / 2.4 h | 0.032 / 2.1 h | 0.028 / 1.9 h |
| 2 | 0.102 / 6.8 h | 0.085 / 5.7 h | 0.073 / 4.8 h | 0.064 / 4.2 h | 0.057 / 3.8 h |
| 3 | 0.153 / 10.2 h | 0.127 / 8.5 h | 0.109 / 7.3 h | 0.095 / 6.4 h | 0.085 / 5.7 h |
| 4 | 0.204 / 13.6 h | 0.170 / 11.3 h | 0.145 / 9.7 h | 0.127 / 8.5 h | 0.113 / 7.5 h |
| 5 | 0.255 / 17.0 h | 0.212 / 14.1 h | 0.182 / 12.1 h | 0.159 / 10.6 h | 0.141 / 9.4 h |
| 6 | 0.305 / 20.4 h | 0.255 / 17.0 h | 0.218 / 14.5 h | 0.191 / 12.7 h | 0.170 / 11.3 h |
Worked examples
Example 1: man, 70 kg, 2 standard drinks, 1 hour. Alcohol is 28 g. Peak = 28 Γ· (70 Γ 1000 Γ 0.68) Γ 100 = 0.0588%. Subtract 0.015 Γ 1 and the estimate is 0.0438%. The theoretical time to zero from the peak is 0.0588 Γ· 0.015 β 3.9 hours.
Example 2: woman, 60 kg, 3 standard drinks, 2 hours. Alcohol is 42 g. Peak = 42 Γ· (60 Γ 1000 Γ 0.55) Γ 100 = 0.1273%. Subtract 0.015 Γ 2 = 0.03 and the estimate is 0.0973%, with about 8.5 hours to zero in theory. Notice that after three drinks the formula still shows a substantial value two hours later.
Example 3: man, 85 kg, 4 standard drinks, 3 hours. Alcohol is 56 g. Peak = 56 Γ· (85 Γ 1000 Γ 0.68) Γ 100 = 0.0969%. Subtract 0.045 and the estimate is 0.0519%, roughly 6.5 hours to zero. Whether such a figure is above or below any legal limit does not matter here: legal limits differ by country, state and type of driver, and the estimate cannot establish where you actually stand.
Why you must not use this to decide about driving
- People differ a lot. Body fat, liver enzyme activity, genetics, medication and fatigue all change r and Ξ². Two people of the same weight who drink the same amount can end up with very different levels.
- Absorption speed is ignored. On an empty stomach alcohol is absorbed quickly and the peak is higher; with food the peak is lower and later. Strong drinks consumed fast produce a sharper peak than the same alcohol sipped slowly.
- Inputs are unreliable. Glass sizes, refills, the real strength of a drink and your memory of timing are all uncertain, and small input errors can produce large output errors.
- Impairment does not begin at a legal limit. Reaction time, attention and judgment can be affected at lower concentrations. Being under a limit is not the same as being safe to drive.
- The law uses official measurement. Enforcement relies on breath or blood tests, never on an online estimate.
- The error can run in the unsafe direction. Because the formula subtracts elimination from the first minute, it can undershoot while alcohol is still being absorbed.
Legal limits for driving differ from country to country, and in some places from region to region or by category of driver, so this page does not state a figure that you should treat as "allowed". Check your local rules, and treat the simple rule as the only safe one: do not drive after drinking. Use this tool to learn how weight, sex and amount interact, not to time your next drive.
Common myths
- Coffee, a big meal or a shower sobers you up. They can change how awake you feel. The liver still works at its own pace, so the blood level falls at about the same speed.
- Sleeping it off is quick. Sleep does not accelerate elimination. After heavy drinking late at night, a substantial amount can remain in the morning.
- Beer is mild. A 500 ml beer at 5% holds about 19.7 g of alcohol, more than one standard drink. Volume matters as much as strength.
- High tolerance means a lower level. Tolerance dulls how drunk you feel, not what a breath or blood test reads. It can make you underestimate your impairment.
When this estimate is not appropriate
If you are pregnant, have liver disease, take medication that interacts with alcohol, or are concerned about your drinking, a general formula is not meaningful and may give false reassurance. Speak to a doctor or a local support service. For healthy-drinking guidance, consult your national health authority's current recommendations.
Using the result sensibly
Use the stat chips to compare scenarios: change the weight or sex to see how strongly they influence the number, or compare two drinks of equal volume but different strength using the serving table. Plan transport before you start drinking, not after. This page is educational information only and is not medical or legal advice. The values you type stay in your browser and are not sent anywhere.
Frequently Asked Questions
Can I use this result to decide whether I can drive?
No. It is a rough estimate based on average values, and individual differences, absorption speed and input errors can make the real level very different. Official decisions use breath or blood tests. If you have been drinking, do not drive.
What is a standard drink in this tool?
It is 14 g of pure alcohol, roughly a 355 ml beer at 5% or a 150 ml glass of wine at 12%. Countries define a standard drink differently, so use the serving table to convert what you actually drank into grams.
Why does the same amount give a higher number for women?
The formula uses a smaller distribution ratio for women on average (0.55 versus 0.68), reflecting lower body-water share. That is an average; individual values differ.
Does eating while drinking change the result?
Food tends to slow absorption and lower the peak, but this calculator does not model it, so it ignores food entirely.
Could I still have alcohol in my blood the next morning?
Yes. If you drank a lot late into the night, the theoretical clearance time in the tables can run past eight or ten hours, and real times vary by person. This is another reason not to rely on an estimate when planning to drive.
Related tools
- BMI Calculator: how body size relates to height and weight.
- Body Fat Calculator: body composition influences how alcohol is distributed.
- Water Intake Calculator: a daily hydration estimate.
- Calorie Calculator: estimate daily energy needs.