BAC calculator

The calculator estimates blood alcohol with the Widmark formula. At 14 g of ethanol, 70 kg, and r = 0.68, BAC is 0.029%. Each hour since the drink subtracts 0.015% BAC, and the result does not go below zero.

This is an estimate, not a breathalyzer reading. The calculator does not say whether you may drive. For weight and height, use the BMI calculator.

Inputs

Mass and drink

Drink

At 0 hours, nothing is subtracted from the Widmark result. Each hour subtracts 0.015% BAC, and the result does not go below zero.

Adjust the factor r

Activity adds from 0 to 0.04 to the factor r. This adjustment does not describe how the liver works.

Result

Enter a weight, choose a drink, and click Calculate. The BAC estimate will appear here.

How it works

14 g of ethanol is 0.029% BAC
Ethanol14 g
Mass70 kg
r0.68
BAC0.029%

The calculator divides grams of ethanol by body mass times the factor r. For a man, r starts at 0.68. For a woman, it starts at 0.55. In the section “Adjust the factor r”, activity adds from 0 to 0.04. At 14 g of ethanol, 70 kg, and a sedentary man, r is 0.68 and BAC is 0.029%.

The calculator multiplies milliliters by the strength in percent and by 0.789 g/ml. When the volume field is in fluid ounces, it converts them to milliliters, because 1 fl oz is 29.5735 ml. A 12 fl oz beer at 5% is about 14 g of ethanol. At the same 70 kg and r = 0.68, BAC is 0.029%. If you already know how much ethanol you had, enter it in the grams field.

Each hour since the drink subtracts 0.015% BAC, and the result does not go below zero. At 0 hours, the result is only the Widmark estimate. The calculator treats the ethanol as already in the body. The calculator does not account for absorption time or a meal.

Permille and BAC percent are the same concentration. 0.029% is 0.29‰. Most US states use 0.08% BAC as the driver limit, and Utah uses 0.05%. In Poland the blood thresholds are 0.2‰ and 0.5‰. The mark on the scale is 0.08%. The calculator does not say whether you may drive.

The units switch converts pounds to kilograms using 0.453592, and then the calculator divides grams by mass and r. The same serving still has the same grams of ethanol.

Formula

permille = grams of ethanol / (mass × r)

BAC percent is permille divided by 10. Grams from a drink are milliliters times the strength in percent times 0.789. When the volume field is in fluid ounces, the calculator converts them to milliliters, because 1 fl oz is 29.5735 ml. For a man, r starts at 0.68. For a woman, it starts at 0.55. With a sedentary lifestyle, r does not change. Light activity adds 0.01, moderate activity adds 0.02, an active lifestyle adds 0.03, and a very active lifestyle adds 0.04. Each hour subtracts 0.015% BAC, and the result does not go below zero. At 14 g, 70 kg, and r = 0.68, with no hours subtracted, BAC is 0.029%.

How to use

  1. Enter body mass in the unit selected at the top of the page.
  2. Choose beer, wine, spirits, or grams. The calculator fills the volume in the unit selected at the top of the page and sets that drink's strength. Beer is 12 fl oz at 5%, wine is 5 fl oz at 12%, and spirits are 1.5 fl oz at 40%. Choosing beer, wine, or spirits does not change the number of servings.
  3. Enter hours since the drink. At 0 hours, nothing is subtracted from the Widmark result. Each hour subtracts 0.015% BAC, and the result does not go below zero.
  4. Choose sex and click Calculate. In the section “Adjust the factor r”, activity changes r only slightly.
  5. Read the estimate. The line on the scale is the 0.08% limit used in most states. The calculator does not say whether you may drive.

BAC and r

The estimate divides grams of ethanol by body mass and the factor r. At 14 g, 70 kg, and r = 0.68, BAC is 0.029%.

Widmark
The formula divides grams of ethanol by mass and the factor r. At 14 g, 70 kg, and r = 0.68, BAC is 0.029%.
Ethanol
Grams of pure ethanol. A 12 fl oz beer at 5% is about 14 g. At 70 kg and r = 0.68, BAC is 0.029%.
Permille
The ‰ unit. 0.29‰ is 0.029% BAC. 0.1‰ is 0.01%.
BAC
Blood alcohol concentration in percent. 0.029% is the same result as 0.29‰. A 0.08% limit equals 0.80‰.
r
The distribution factor. For a man, r starts at 0.68, and for a woman at 0.55. Activity adds a small adjustment, and r stays between 0.50 and 0.75.
Hour
Each hour subtracts 0.015% BAC, and the result does not go below zero. At 0 hours, the result is only the Widmark estimate. The calculator treats the ethanol as already in the body.
Limit
Most US states use 0.08% BAC for drivers. Utah uses 0.05%. In Poland the blood thresholds are 0.2‰ and 0.5‰. The mark on the scale is only a reference. It is not a decision about driving.

One beer, two legal lines

A 12 fl oz beer at 5% alcohol by volume is about 14 g of ethanol. At 70 kg and r = 0.68, BAC is 0.029%. Most US states set the driver limit at 0.08% BAC. Utah uses 0.05%. This estimate is under both of those limits.

The same result is 0.29‰. In Poland the lower blood-alcohol threshold is 0.2‰, and the higher one is 0.5‰. In this estimate, one US beer is above Poland's 0.2‰ threshold and still under 0.08% BAC. Two of those beers are 0.059% BAC, still under 0.08%. That is 0.59‰, above Poland's 0.5‰ threshold.

A 500 ml can at 5%, a common European size, is about 19.7 g and 0.041% BAC at the same mass. Two of those cans are 0.083% BAC. Each hour subtracts 0.015% BAC, and the result does not go below zero. The calculator treats the ethanol as already in the body. The calculator does not account for absorption time or a meal. The calculator does not measure breath and does not say whether you may drive.

A beer on the BAC scale One 12 fl oz beer at 5% is 0.029% BAC. Two are 0.059%. The line at 0.08% is the limit in most states. 12 fl oz · 5% 14 g 1 beer 0.029% 2 beers 0.059% 0 0.08% 0.10%
One 12 fl oz beer at 5% is 0.029% BAC at 70 kg and r = 0.68. Two of those beers are 0.059%. The line at 0.08% is the limit in most states.

When you click the button, the calculator fills the mass, sex, and activity from this description and sets hours to 0. One beer is one serving, and two beers are two servings.

Examples

Each example sets hours since the drink to 0.

Example 1

  • Weight: 70 kg
  • Ethanol: 14 g
  • Sex: male
  • Activity: sedentary

0.029%

At 14 g of ethanol, 70 kg, and r = 0.68, BAC is 0.029%.

Example 2

  • Weight: 70 kg
  • Ethanol: 20 g
  • Sex: male
  • Activity: sedentary

0.042%

At the same 70 kg and the same sedentary man, 20 g of ethanol is 0.042% BAC.

Example 3

  • Weight: 60 kg
  • Ethanol: 10 g
  • Sex: female
  • Activity: sedentary

0.030%

At 60 kg, 10 g, and a sedentary woman, BAC is 0.030%, because r is 0.55.

Example 4

  • Weight: 80 kg
  • Ethanol: 20 g
  • Sex: male
  • Activity: moderate

0.036%

At 80 kg, 20 g, and moderate activity, r is 0.70 and BAC is 0.036%.

Example 5

  • Weight: 90 kg
  • Ethanol: 14 g
  • Sex: male
  • Activity: sedentary

0.023%

At 90 kg and 14 g for a sedentary man, BAC is 0.023%.

Example 6

  • Weight: 55 kg
  • Ethanol: 20 g
  • Sex: female
  • Activity: sedentary

0.066%

At 55 kg, 20 g, and a sedentary woman, BAC is 0.066%, because r is 0.55.

Example 7

  • Weight: 75 kg
  • Ethanol: 10 g
  • Sex: male
  • Activity: light

0.019%

At 75 kg, 10 g, and light activity, r is 0.69 and BAC is 0.019%.

Example 8

  • Weight: 65 kg
  • Ethanol: 14 g
  • Sex: female
  • Activity: moderate

0.038%

At 65 kg, 14 g, and moderate activity, r is 0.57 and BAC is 0.038%.

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Frequently asked questions

Does this calculator replace a breathalyzer?

No. The calculator estimates concentration from grams of ethanol and body mass. A breathalyzer measures breath. This page does not say when you may drive.

Where does 0.029% BAC come from at 14 g?

The calculator divides grams of ethanol by body mass times the factor r. At 14 g, a mass of 70 kg, and r = 0.68, BAC is 0.029%, which is 0.29‰. At 0 hours, the calculator subtracts nothing from that.

How do permille and BAC percent relate?

They are two scales for the same concentration. 0.029% is 0.29‰. A 0.08% BAC limit equals 0.80‰. Poland's 0.2‰ threshold is 0.02% BAC.

How do I enter a beer?

Choose Beer. The calculator fills the volume in the unit selected at the top of the page and sets the strength to 5%. That beer is 12 fl oz and about 14 g of ethanol. At 70 kg and r = 0.68, BAC is 0.029%. A volume you type yourself stays in the field until you choose beer, wine, or spirits.

What is the activity field for?

Activity adds from 0 to 0.04 to the factor r. At 80 kg, 20 g, a man, and moderate activity, r is 0.70 and BAC is 0.036%. This adjustment does not describe how the liver works.

May I drive at 0.029% BAC from one beer?

The calculator does not answer that. 0.029% is under the 0.08% line used in most states, and it is still an estimate, not a measurement. If you are not sure, do not drive.

Does a different mass unit change the result?

No. The switch converts the same body mass, so the estimate stays. A different mass that you type gives a different result.

Does time since the drink lower the result?

Yes, by 0.015% BAC for each hour. The result does not go below zero. At 0 hours, the result is only the Widmark estimate. The calculator does not account for absorption time or a meal.

· Hubert Ligocki

The result is a BAC estimate for the mass and ethanol grams you enter. At 14 g, 70 kg, and r = 0.68, it is 0.029%.

Knowledge sources

The estimate uses the Widmark formula: grams of ethanol divided by mass and the factor r. This is not a breathalyzer reading.

Page updated October 1, 2026.