# BAC Calculator (Blood Alcohol Content)

URL: https://speedycalculator.com/calculators/health/bac/
Last updated: 2026-10-30

> The BAC calculator estimates your blood alcohol concentration with the Widmark formula from the drinks you had, your sex, body weight and the time since you started drinking, and shows how long until your BAC returns to zero. Never use it to decide whether you can drive.

## Inputs

- Sex
- Weight (kg, lb, st, g)
- Beer, 12 oz (355 ml) at 5%
- Large beer, pint (473 ml) at 5%
- Wine, 5 oz (148 ml) at 12%
- Spirits shot, 1.5 oz (44 ml) at 40%
- Other drink – total volume (mL, L, fl oz)
- Other drink – alcohol by volume (%)
- Hours since your first drink

## Results

- Alcohol consumed
- US standard drinks (14 g)
- Estimated BAC
- Time until BAC reaches zero
- Time until below 0.08%
- Time until below 0.05%

## Formula

```
Alcohol (g) = Σ volume × ABV × 0.789
BAC (%) = alcohol (g) ÷ (body weight (g) × r) × 100 − 0.015 × hours
r (Widmark factor) = 0.68 for men, 0.55 for women
```

## Explanation

Erik Widmark worked out in the 1930s how alcohol spreads through body water and is removed by the liver at a fairly steady rate – about 0.015% per hour. Real BAC depends on food, drinking speed, medicines and individual metabolism, so the estimate can be off by a large margin. The only safe level for driving is zero.

### How to use the BAC Calculator

- **Sex**
- **Weight**
- **Beer, 12 oz (355 ml) at 5%**
- **Large beer, pint (473 ml) at 5%**
- **Wine, 5 oz (148 ml) at 12%**
- **Spirits shot, 1.5 oz (44 ml) at 40%**
- **Other drink – total volume**
- **Other drink – alcohol by volume**
- **Hours since your first drink**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter how many of each drink you had, any other drink by volume and strength, your weight and sex, and the hours since your first drink.

### Effects of BAC

BACTypical effects0.02–0.05%Relaxation, reduced judgement and coordination0.05–0.08%Impaired reaction time and driving skills0.08–0.15%Clear impairment of balance, speech and vision0.15–0.30%Major loss of control, vomiting, blackoutsAbove 0.30%Risk of loss of consciousness and death

### Inputs explained

FieldWhat to enterSexChoose one: Male, FemaleWeightUnits: kg, lb, st, gBeer, 12 oz (355 ml) at 5%A numberLarge beer, pint (473 ml) at 5%A numberWine, 5 oz (148 ml) at 12%A numberSpirits shot, 1.5 oz (44 ml) at 40%A numberOther drink – total volumeUnits: mL, L, fl ozOther drink – alcohol by volumeIn %Hours since your first drinkA number

### What each result means

- **US standard drinks (14 g)** = [Alcohol consumed]÷14
- **Time until BAC reaches zero** = [Estimated BAC]÷0.015
- **Time until below 0.08%** = max([Estimated BAC] - 0.08, 0)÷0.015
- **Time until below 0.05%** = max([Estimated BAC] - 0.05, 0)÷0.015

*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — Sex: Male; Weight: 80 kg; Beer, 12 oz (355 ml) at 5%: 2; Large beer, pint (473 ml) at 5%: 0; Wine, 5 oz (148 ml) at 12%: 0; Spirits shot, 1.5 oz (44 ml) at 40%: 0; Other drink – total volume: 0 mL; Other drink – alcohol by volume: 13 %; Hours since your first drink: 2.

Results — Alcohol consumed = 28 g; US standard drinks (14 g) = 2; **Estimated BAC = 0.021 %**; Time until BAC reaches zero = 1 h 26 min; Time until below 0.08% = 0 h 0 min; Time until below 0.05% = 0 h 0 min.

## Key terms

- **BAC**: Blood alcohol concentration, grams of alcohol per 100 mL of blood (%).
- **Widmark factor**: Share of body weight in which alcohol distributes.

## FAQ

**How accurate is a BAC calculator?**
It is a rough estimate; real BAC can be much higher, especially on an empty stomach.

**What is the legal driving limit?**
0.08% in the US (Utah 0.05%) and UK (except Scotland, 0.05%); 0.05% in most of Europe and Australia; zero for new or commercial drivers in many places.

**Does coffee or a cold shower sober you up?**
No – only time lowers BAC.

**When is alcohol poisoning an emergency?**
Confusion, vomiting, seizures, slow breathing or unconsciousness – call emergency services.


## Sources

- [NIAAA – Understanding alcohol's effects](https://www.niaaa.nih.gov/alcohols-effects-health)
- Widmark EMP. Principles and applications of medicolegal alcohol determination, 1932 (English translation 1981)