Blood Alcohol Calculator

Estimate your blood alcohol content (BAC) using the Widmark formula. The South African legal driving limit is 0.05 g/100ml. For awareness only — never drink and drive.

⚡ Quick Calculator Get a fast estimate

Gender

Body Weight

Standard Drinks Consumed

drinks

1 standard drink = 340ml beer (5%) or 150ml wine (12%) or 44ml spirits (40%)

Hours Since First Drink

hrs

Blood Alcohol Content (BAC)

0,04 g/100ml

Status

Below SA legal driving limit (0.05 g/100ml)

SA Legal Driving Limit

0.050 g/100ml

Estimated Time to Legal Limit

Already at or below limit

Estimated Time Until Sober (BAC = 0)

~2,7 hours

Disclaimer

Estimates only. Never drive after drinking alcohol.

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How to Use the Blood Alcohol Calculator

Select your gender, enter your body weight, the number of standard drinks consumed, and how many hours have passed since your first drink. The Widmark formula estimates your current BAC and tells you how it compares to South Africa's legal driving limit of 0.05 g/100ml.

This calculator provides estimates only. Individual alcohol metabolism varies. Never drive after consuming any alcohol.

The Extended Calculator below shows a BAC-over-time chart and includes an "Evening Out" scenario planner with SA legal limit warnings. The Professional Calculator adds a multi-drink timeline, body-type metabolism rates, and an hourly BAC forecast table.

Need more detail?

📊 Extended Calculator More options, charts, and scenario comparison

Body Weight

Sex

Drinks

13g alc

17g alc

Peak BAC

0.043 g/100ml

SA legal limit

0.05 g/100ml

Prof. drivers limit

0.02 g/100ml

Below legal limit

0.3h

Fully sober

4.3h

BAC Over Time

Disclaimer: This calculator provides estimates only. Many factors affect BAC. Never drink and drive. South African BAC legal limit: 0.05g/100ml for regular drivers, 0.02g/100ml for professional drivers and those under 25.

Widmark Formula

BAC = (Grams of Alcohol ÷ (Body Weight kg × r × 10)) − (0.015 × Hours)

r (Widmark factor): 0.68 for men | 0.55 for women

Elimination rate: approximately 0.015 g/100ml per hour

Result is expressed in g/100ml (same unit as SA law).

What Is a Standard Drink?

1 standard drink = 14 g of pure alcohol:

340 ml beer at 5% ABV

150 ml wine at 12% ABV

44 ml (1.5 tots) spirits at 40% ABV

South African Law

Legal limit: 0.05 g/100ml blood (National Road Traffic Act)

Professional drivers: 0.02 g/100ml

Penalty: Up to 6 years imprisonment for drunk driving causing death.

There is no safe amount of alcohol for driving. The only safe choice is zero alcohol.

Need full precision?

🔬 Professional Calculator Complete parameters, sensitivity analysis, and detailed breakdown

Profile

Weight

Sex

Body Type

Food Consumed

Drink Timeline

ml ath

Peak BAC

0.042 g/100ml

Peak at

+3.0h

Total units

8.2

Elimination rate

0.015/h

Below 0.05 at

+0.3h

Fully sober at

+4.5h

Hourly BAC Forecast

Time	BAC g/100ml	Status
+0h	0.031	Below general limit
+1h	0.016	Below prof. limit
+2h	0.020	Below general limit
+3h	0.042	Below general limit
+4h	0.007	Below prof. limit
+5h	0.000	Sober
+6h	0.000	Sober
+7h	0.000	Sober
+8h	0.000	Sober
+9h	0.000	Sober
+10h	0.000	Sober
+11h	0.000	Sober
+12h	0.000	Sober
+13h	0.000	Sober
+14h	0.000	Sober
+15h	0.000	Sober
+16h	0.000	Sober
+17h	0.000	Sober

Important: Never drink and drive. This is an estimation tool only. Individual metabolism varies. If in doubt, don't drive. BAC can continue rising for 30–120 minutes after your last drink.

Frequently Asked Questions

The liver metabolises alcohol at a rate of approximately 0.015 g/100ml per hour — equivalent to roughly one standard drink per hour. This rate cannot be sped up by coffee, exercise, or cold showers. Only time eliminates alcohol from your blood.

Women generally have a lower percentage of body water (r factor: 0.55 vs 0.68 for men), meaning the same amount of alcohol is distributed in less fluid and produces a higher BAC. Women also have lower levels of alcohol dehydrogenase, the enzyme that breaks down alcohol in the stomach.

Even below 0.05 g/100ml, alcohol impairs reaction time, concentration, and judgment. South Africa's Road Traffic Management Corporation strongly advises zero alcohol before driving. This calculator is for awareness only and its output should never be used to justify driving after drinking.

Eating before or during drinking slows alcohol absorption into the bloodstream, reducing the peak BAC. However, food does not speed up the elimination of alcohol already in your system. If you have been drinking, the only remedy is time.