Blood alcohol content (BAC) calculator
Estimate your blood alcohol content with the Widmark formula, in g/L and %. An estimate only — never drink and drive.
⚠️ Widmark-formula estimate — the real value varies with metabolism, food and other factors. Never drink and drive.
How the calculation works
It uses the Widmark formula: C = A ÷ (r × weight) − β × t. A is the mass of pure alcohol (volume × ABV × 0.789), r the distribution factor (0.68 men / 0.55 women) and β ≈ 0.15 g/L per hour the elimination. Result is in g/L; divided by 10 it becomes the US "%" (0.8 g/L = 0.08%).
Examples
- One beer (350 ml, 5%) in an 80 kg man: ~0.25 g/L right after, dropping ~0.15 g/L per hour.
- In Brazil the driving limit is ZERO — any value is an offense.
Frequently asked questions
Can I rely on this to decide to drive?
No. It is an educational estimate only. If you have been drinking, do not drive.
How long until it reaches zero?
The body eliminates about 0.15 g/L per hour, but it varies a lot between people.
Do coffee or a cold shower speed elimination?
No. Only time removes alcohol — the liver works at a nearly fixed rate. Coffee may make you more alert but does not lower blood alcohol.
Can I use this to decide whether to drive?
No. The formula is a population average and real values vary widely. If you drank, do not drive.
What are the drink-driving limits in Brazil?
On a breath test, up to 0.04 mg/L is no offence; from 0.05 mg/L it is a severe administrative offence; from 0.34 mg/L it becomes a criminal offence.
Can I drive the next morning?
Not always. Elimination is slow: 0.8 g/L takes over five hours to clear, so morning driving can still be an offence.
Sources and references
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Updated on June 30, 2026 · by Rafael Rossi · Methodology & sources