ExactUnits
↑↓ move ↵ open Esc close All shortcuts

Blood alcohol content calculator

The Widmark equation is the standard forensic estimate. It is an estimate: real BAC depends on stomach contents, drinking speed and individual physiology.

One US standard drink is 14 g of pure alcohol.

g
hours
Estimated BAC
0.0582% w/v
= Exact Over the limit in most US states
Peak BAC if all absorbed at once
0.0882 % w/v
Hours until zero from now
3.88
Total alcohol consumed
42.0 g
Show the working
  1. Standard drinks = 3
  2. Alcohol per drink = 14
  3. Body weight = 70
  4. Sex = 1
  5. Hours since the first drink = 2
  6. Total alcohol consumed = 3 * 14 = 42
  7. r = 1 > 0 ? 0.68 : 0.55 = 0.68
  8. Peak BAC if all absorbed at once = 42 / (70 * 1000 * 0.68) * 100 = 0.088 235 3
  9. Estimated BAC = max(0, 0.088 235 3 - 0.015 * 2) = 0.058 235 3
  10. Hours until zero from now = 0.088 235 3 / 0.015 - 2 = 3.882 35
  11. over_limit = 0.058 235 3 >= 0.08 ? 1 : 0 = 0

Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.

Scenarios & local history

Compare a saved scenario

Recent calculations

    The formula

    • BAC = alcohol in grams / (body mass in grams x r) x 100, with r = 0.68 for men and 0.55 for women
    • Elimination proceeds at roughly 0.015 percentage points per hour.

    Never use this to decide whether to drive. Individual variation is large, absorption is not instantaneous, and being under a legal limit is not the same as being safe.

    The Widmark factor r represents the fraction of body mass that behaves like water for alcohol distribution.

    This is a population formula, not a diagnosis. Individual metabolism, body composition and medical history all move the real answer, so treat the number as a starting point and talk to a clinician about anything that matters.

    Related calculators

    Settings

    Theme

    System follows your operating system and changes with it.

    Text size
    High contrast

    Maximises text and border contrast and removes the grid background.

    Graph-paper background
    Round to
    Notation
    Thousands separators
    Decimal mark
    Nearest fraction

    Shows the result as the nearest tape-measure fraction, with the error it costs.

    Accessibility & interaction
    Reduce motion Stops interface animations even when the operating system does not.
    Underline links Keeps links visually distinct without relying on colour.
    Larger touch targets Makes buttons and form controls easier to tap.
    Shorter reading lines Limits article width for easier scanning.
    Monochrome display Removes colour as an information cue.
    Always-visible focus Makes the keyboard focus ring persistent and stronger.
    Verbose screen-reader results Announces the complete conversion equation.
    Sticky action bars Keeps converter and calculator actions within reach.
    Select values on focus Replaces a value immediately when you start typing.
    Left-handed mobile layout Moves key mobile actions toward the left thumb.
    Your data

    Settings, recent conversions and favourites live in this browser only. Nothing is sent anywhere.

    Offline library