BAC Calculator — Blood Alcohol Estimate (Widmark)

How this calculator works

It uses the Widmark formula, the classic method for estimating blood alcohol:

• BAC (%) = alcohol (g) ÷ (body weight (g) × r) × 100 − 0.015 × hours
• r (the body-water distribution factor) = 0.68 for men and 0.55 for women, Widmark's average values
• Alcohol (g) = standard drinks × 14 g, or drinks × size (mL) × ABV × 0.789
• 0.015% per hour is a commonly used, conservative elimination rate; measured rates vary widely between people (roughly 0.009–0.035% per hour)

By Suhaib Hassan · Reviewed 28 September 2026 against NIAAA and NHTSA information · How CalculatePilot verifies formulas →

A worked example

A 176 lb (80 kg) man who has had 4 standard drinks (56 g of alcohol) over 2 hours: 56 ÷ (80,000 × 0.68) × 100 = 0.103%, minus 0.015 × 2 = about 0.073%. At 0.015% an hour, it would take roughly another 5 hours to fall to zero.

This is an estimate — not a safety determination

Real BAC depends on food, drinking speed, medications, health, body composition and individual metabolism, so your true BAC could be higher or lower than this estimate. Alcohol also keeps being absorbed for a while after your last drink, so BAC can still be rising. Impairment starts well below legal limits: NHTSA notes that even at 0.02% people show some loss of judgment and a decline in the ability to do two things at once. No calculator can tell you it's safe to drive. If you've been drinking, use a rideshare, taxi, public transport or a sober designated driver.

This page uses US figures. The legal limit for drivers 21 and over is 0.08% in every US state except Utah (0.05%); commercial drivers are limited to 0.04%, and drivers under 21 face zero-tolerance laws. Limits differ in other countries, and being under a limit does not mean you are safe to drive.

Sources

• Widmark EMP. Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung. Berlin: Urban & Schwarzenberg, 1932.
• Jones AW. Evidence-based survey of the elimination rates of ethanol from blood with applications in forensic casework. Forensic Science International 2010;200:1–20.
• NIAAA — What is a standard drink?
• NHTSA — Drunk Driving

BAC chart by weight and number of drinks

Estimated peak BAC from the Widmark formula with no time passed and nothing eliminated, so these are the highest values. Standard drinks of 14 g of alcohol each. Estimates only.

Men (r = 0.68)

Weight	1 drink	2	3	4	5
120 lb	0.038%	0.076%	0.113%	0.151%	0.189%
140 lb	0.032%	0.065%	0.097%	0.130%	0.162%
160 lb	0.028%	0.057%	0.085%	0.113%	0.142%
180 lb	0.025%	0.050%	0.076%	0.101%	0.126%
200 lb	0.023%	0.045%	0.068%	0.091%	0.113%

Women (r = 0.55)

Weight	1 drink	2	3	4	5
120 lb	0.047%	0.094%	0.140%	0.187%	0.234%
140 lb	0.040%	0.080%	0.120%	0.160%	0.200%
160 lb	0.035%	0.070%	0.105%	0.140%	0.175%
180 lb	0.031%	0.062%	0.094%	0.125%	0.156%
200 lb	0.028%	0.056%	0.084%	0.112%	0.140%

How many drinks to reach 0.08%?

The number of standard drinks that brings the peak estimate (no elimination) to the 0.08% US driving limit:

Weight	Men	Women
120 lb	2.1	1.7
140 lb	2.5	2.0
160 lb	2.8	2.3
180 lb	3.2	2.6
200 lb	3.5	2.9

Drinking over time lowers the real figure, but impairment starts well below 0.08%. Never use this to decide whether to drive.

Time for BAC to fall to zero

At the calculator's conservative rate of 0.015% an hour:

BAC	Time to 0.00%
0.04%	2.7 hours
0.08%	5.3 hours
0.10%	6.7 hours
0.15%	10.0 hours
0.20%	13.3 hours

Measured elimination rates vary roughly between 0.009% and 0.035% an hour, so the true time can be much longer or shorter.

US driving limits

Driver	Limit
21 and over (all states except Utah)	0.08%
Utah	0.05%
Commercial drivers	0.04%
Under 21	Zero tolerance laws

Being under a limit does not mean you are safe to drive.

Frequently asked questions

How accurate is a BAC calculator?expand_more

It gives a rough, population-average estimate. Two people drinking the same amount can have very different BACs because of food, drinking speed, body composition, medications and metabolism. Only a breath or blood test measures BAC.

How long does it take for BAC to reach zero?expand_more

The body removes alcohol at a commonly estimated rate of about 0.015% per hour (a conservative figure; measured rates vary widely between people, roughly 0.009–0.035% per hour), and nothing — coffee, cold showers or exercise — speeds this up. A BAC of 0.08% takes about 5 hours or more to clear.

What counts as a standard drink?expand_more

In the US, a standard drink contains about 14 grams (0.6 fl oz) of pure alcohol — roughly a 12-oz beer at 5%, a 5-oz glass of wine at 12%, or a 1.5-oz shot of 40% spirits. Craft beers, large pours and cocktails often contain more.

How many drinks does it take to reach 0.08% BAC?expand_more

It depends on weight and sex. For a 160 lb man the peak estimate reaches 0.08% at about 2.8 standard drinks, and for a 160 lb woman at about 2.3. Drinking slowly lowers the real figure, but impairment starts earlier.

What is the Widmark formula?expand_more

BAC = alcohol in grams divided by (body weight in grams times r), times 100, minus elimination over time. R is 0.68 for men and 0.55 for women, and elimination is estimated at 0.015% per hour.

Why is the estimate higher for women at the same weight?expand_more

The Widmark factor r is lower for women (0.55 against 0.68), which reflects a lower average share of body water, so the same alcohol gives a higher concentration.

What is the legal BAC limit in the US?expand_more

0.08% for drivers 21 and over in every state except Utah, which uses 0.05%. Commercial drivers are limited to 0.04% and drivers under 21 face zero tolerance laws.

Can I use a BAC calculator to decide if I can drive?expand_more

No. It is an educational estimate, and impairment begins below the legal limits. If you have been drinking, use a taxi, rideshare, public transport or a sober driver.