How is BAC estimated?

The Widmark formula estimates BAC as alcohol grams ÷ (body weight in grams × r) × 100, where r is a distribution ratio (about 0.68 for men and 0.55 for women). It then subtracts roughly 0.015% per hour for the alcohol your body eliminates over time.

Can I rely on this to decide whether to drive?

Absolutely not. This is an educational estimate only. Actual BAC varies enormously with food, hydration, medication, metabolism, health and the exact drink strength. If you have been drinking, do not drive — the only safe amount before driving is none.

How much alcohol is in one drink?

It depends on the drink and country. A UK unit contains about 8 g of pure alcohol; a US standard drink about 14 g. A pint of 5% beer is roughly 2.3 UK units (about 18 g), and a 175 ml glass of 13% wine about 2.3 units. Enter the grams per drink that match what you drank.

How long does alcohol take to leave the body?

The body eliminates alcohol at roughly 0.015% BAC per hour and this rate cannot be sped up by coffee, food or a cold shower. The calculator estimates the hours until your BAC returns to about zero, but individual rates vary.

Completely. Every figure is calculated inside your browser and nothing you enter is sent to a server or stored.

What is the Blood Alcohol Calculator (BAC)?

Free blood alcohol content (BAC) estimator using the Widmark formula. Enter your body weight, sex, number of drinks and time elapsed to estimate your blood alcohol concentration. For education only — never use to decide whether to drive. Runs entirely in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Blood Alcohol Calculator (BAC)

Name: Blood Alcohol Calculator (BAC)
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Blood alcohol calculator — a Widmark BAC estimate

This tool gives an educational estimate of blood alcohol concentration (BAC) from the number of drinks, your body weight and sex, and the time since your first drink, using the well-known Widmark formula. It is for understanding how alcohol behaves in the body — not a tool for deciding whether it is safe to drive.

How it works

The Widmark formula estimates peak BAC as alcohol grams ÷ (body weight in grams × r) × 100, where r is a distribution ratio (about 0.68 for men, 0.55 for women). The body then eliminates alcohol at roughly 0.015% BAC per hour, which the tool subtracts based on the time elapsed.

Worked example

An 80 kg man who has had 3 drinks of 10 g alcohol each, 2 hours ago:

Alcohol consumed: 3 × 10 = 30 g
Peak BAC: 30 ÷ (80,000 × 0.68) × 100 ≈ 0.055%
After 2 hours: 0.055 − (0.015 × 2) = 0.025%

Important safety note

BAC estimates like this can be wrong by a wide margin for any individual because food, hydration, medication, metabolism, health and the true strength of each drink all change the result. Never use this or any calculator to decide whether to drive. If you have been drinking, do not drive — the only safe level before driving is zero. Legal limits differ by country and are not the same as “safe”.

Practical tips

Match the grams to your drinks. A UK unit is about 8 g of alcohol; a US standard drink about 14 g. Stronger or larger serves contain more — enter the grams that reflect what you actually drank.

Time is the only cure. Only time lowers BAC, at about 0.015% per hour. Coffee, water and food do not speed elimination.

All calculations run entirely in your browser — nothing is uploaded or stored.