Skip to content
ENExplore Calculators

Blood Alcohol Content Calculator

Work out blood alcohol content instantly with clear inputs, formula shown and shareable results.

About Blood Alcohol Content Calculator

This is the Widmark equation: BAC = alcohol grams / (body water ratio x body weight in grams), expressed as a percentage, less 0.015 percentage points per hour of elimination. Elimination is nearly constant at about 0.015% an hour regardless of how much was drunk, which is why time is the only thing that lowers BAC.

Formulas

Widmark equation

BAC % = alcohol grams / (r x weight in grams) x 100, with r = 0.68 male or 0.55 female

Elimination

current BAC = peak BAC - 0.015 x hours elapsed

Worked example

With the default values below, Blood Alcohol Content Calculator returns Estimated blood alcohol now of 0.0288%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Body weightminimum 20 kg
70 kg
Sexone of Male (distribution ratio 0.68), Female (distribution ratio 0.55)
Male (distribution ratio 0.68)
Pure alcohol consumedminimum 0.1 g
28 g
Hours since the first drinkminimum 0 h
2 h

Results

Estimated blood alcohol now
0.0288%
Peak blood alcohol
0.0588%
In per mille (g/L)
0.288
Further hours until clear
1.92 h

Step by step

  1. 1Values used
  2. 2Widmark equation
  3. 3Elimination
  4. 4Estimated blood alcohol now= 0.0288
  5. 5Peak blood alcohol= 0.0588
  6. 6In per mille (g/L)= 0.288
  7. 7Further hours until clear= 1.92 h

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Blood Alcohol Content figure worked out?

BAC % = alcohol grams / (r x weight in grams) x 100, with r = 0.68 male or 0.55 female. This is the Widmark equation: BAC = alcohol grams / (body water ratio x body weight in grams), expressed as a percentage, less 0.015 percentage points per hour of elimination.

Why does this matter?

Elimination is nearly constant at about 0.015% an hour regardless of how much was drunk, which is why time is the only thing that lowers BAC.

What do I need to enter?

Enter body weight, sex, pure alcohol consumed, hours since the first drink. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.

Related Calculators

Blood Alcohol Content Calculator | Calcrivo