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BAC Calculator: Blood Alcohol Over Time

Estimate your blood alcohol level from what you’ve had to drink, watch it fall hour by hour to zero, and look up any weight on the BAC by weight chart. Know your limits, plan ahead, and stay safe.

Your estimated BAC
0.055
Mild relaxation

Mild relaxation, slight euphoria, lowered inhibitions.

Nought to 0.40 BAC, always — the axis never rescales
You · 0.055
Under 0.06 0.06 – 0.08 0.08 and over — the US legal limit 0.25 and over

Under the US legal limit of 0.08, and impaired all the same: reaction time and divided attention are measurably worse from about 0.02. Never use this estimate to decide whether to drive.

Back to nought in 3h 41m At the average elimination rate this tool assumes, about 0.015% BAC an hour. Nothing speeds it up.
Which is roughly 12:25 PM On your device’s clock. Individual rates differ, so treat it as the earliest rather than the answer.
Weight
Rounded is fine. A stone either way moves the estimate by a few thousandths, not by a zone.
Biological sex
This picks the Widmark r factor — 0.68 for men, 0.55 for women — because alcohol spreads through body water and the proportion of it differs. The same drinks give a woman a higher BAC at the same weight.
Number of drinks 3 drinks
One standard drink is 12oz of beer, 5oz of wine or 1.5oz of spirits — about 14g of pure alcohol. A large glass of wine is nearer two.
Time spent drinking 2 hours
From the first drink to the last, not the time since you stopped. Your liver has been clearing alcohol the whole way through.
Time since your last drink 0 hours
Leave it at nought for the reading at your last drink. Move it on to see where the estimate stands now.
Cleared.

Your BAC over time

The estimate from your first drink back to zero, on the numbers above.

Hours since your first drink

When it falls under each line

Under 0.08
Never reaches it
Under 0.05
0h 21m from now0h 21m after your last drink
Back to zero
3h 41m from now3h 41m after your last drink

Hour by hour after your last drink

After your last drink Estimated BAC
At the last drink 0.055%
1 hour later 0.040%
2 hours later 0.025%
3 hours later 0.010%
4 hours later 0.000%

The climb assumes your drinks were spread evenly over the time you spent drinking; the fall after the last one is the same 0.015% an hour the rest of this page uses.

Straight lines at an average rate are all the Widmark arithmetic contains. Food, medication, how fast you drank and your own liver move every line on this chart. Falling under a line here cannot tell anyone they are safe to drive.

The impairment scale

BACWhat the research describes at that level
0.00 – 0.029 Subtle effects, minimal impairment. You may feel normal.
0.03 – 0.059 Mild relaxation, slight euphoria, lowered inhibitions.
0.06 – 0.079 Judgment and reasoning affected. Reduced coordination.
0.08 – 0.099 Legally drunk in the US. Balance, speech, and reaction time impaired.
0.10 – 0.149 Significant impairment of motor control. Slurred speech, poor balance.
0.15 – 0.199 Serious impairment. Risk of blackout, nausea, loss of muscle control.
0.20 – 0.249 Dangerous. Confusion, vomiting, risk of injury or aspiration.
0.25+ Life-threatening. Loss of consciousness, alcohol poisoning. Call 911.

BAC by weight chart

Estimated peak BAC by body weight and number of standard drinks of 14 g of alcohol each, if the drinks land together and nothing has cleared yet. Subtract about 0.015 for every hour since the first drink.

Men
Weight Standard drinks
1 2 3 4 5 6 7 8
100 lb 0.045 0.091 0.136 0.182 0.227 0.272 0.318 0.363
120 lb 0.038 0.076 0.113 0.151 0.189 0.227 0.265 0.303
140 lb 0.032 0.065 0.097 0.130 0.162 0.195 0.227 0.259
160 lb 0.028 0.057 0.085 0.113 0.142 0.170 0.199 0.227
180 lb 0.025 0.050 0.076 0.101 0.126 0.151 0.177 0.202
200 lb 0.023 0.045 0.068 0.091 0.113 0.136 0.159 0.182
220 lb 0.021 0.041 0.062 0.083 0.103 0.124 0.144 0.165
240 lb 0.019 0.038 0.057 0.076 0.095 0.113 0.132 0.151
Women
Weight Standard drinks
1 2 3 4 5 6 7 8
100 lb 0.056 0.112 0.168 0.225 0.281 0.337 0.393 0.449
120 lb 0.047 0.094 0.140 0.187 0.234 0.281 0.327 0.374
140 lb 0.040 0.080 0.120 0.160 0.200 0.241 0.281 0.321
160 lb 0.035 0.070 0.105 0.140 0.175 0.210 0.246 0.281
180 lb 0.031 0.062 0.094 0.125 0.156 0.187 0.218 0.249
200 lb 0.028 0.056 0.084 0.112 0.140 0.168 0.196 0.225
220 lb 0.026 0.051 0.077 0.102 0.128 0.153 0.179 0.204
240 lb 0.023 0.047 0.070 0.094 0.117 0.140 0.164 0.187

Widmark estimate with an r of 0.68 for men and 0.55 for women and 14 g of alcohol per standard drink. Real BAC varies with food, medication, genetics and how fast you drank. None of these figures can tell anyone they are safe to drive.

https://getrebuild.app/tools/bac-calculator

Prints on one page: both charts and nothing else from this page.

How this is calculated

This calculator uses the Widmark equation — the standard method for estimating blood alcohol concentration from body weight, biological sex, the amount of pure alcohol consumed, and elapsed time. It assumes a body-water distribution factor (Widmark's "r") of roughly 0.68 for men and 0.55 for women, a US standard drink of 14 g of pure alcohol, and an average elimination rate of about 0.015% BAC per hour. The over-time curve spreads your drinks evenly across the hours you spent drinking and then falls in a straight line at that rate; the by-weight chart shows the peak if every drink landed at once. Promille and grams-per-litre figures are the per-cent figure multiplied by ten. Real BAC varies with genetics, liver function, food, medication and drinking speed, so treat every number here as a rough estimate rather than a measurement.

Sources

Our editorial policy explains how these tools and articles are researched and kept up to date.

Understanding Blood Alcohol Content

The Widmark Formula

This calculator uses the Widmark formula, a well-established method for estimating blood alcohol content developed by Swedish physician Erik Widmark in the 1930s. It remains the standard approach used in forensic toxicology.

The formula accounts for the amount of pure alcohol consumed (each standard drink contains about 14 grams), your body weight, a sex-based distribution ratio (the Widmark r factor: 0.68 for men, 0.55 for women), and the time elapsed while your liver metabolizes alcohol at roughly 0.015% BAC per hour.

The result is an estimate. Real BAC depends on many individual factors this formula cannot capture, so always err on the side of caution.

What Affects Your BAC Besides Drinks

Food intake: Drinking on an empty stomach can produce a BAC up to 3 times higher than drinking after a full meal. Food slows gastric emptying, giving your liver more time to process alcohol before it reaches your bloodstream.

Medications: Many common medications — including antihistamines, antidepressants, painkillers, and antibiotics — can amplify the effects of alcohol or slow its metabolism. Always check drug interactions.

Hydration: Dehydration concentrates alcohol in your blood. Alternating alcoholic drinks with water can slow absorption and reduce peak BAC.

Tolerance vs. BAC: Regular drinkers may feel less impaired, but their BAC is just as high. Tolerance changes how drunk you feel, not how drunk you actually are. This is one of the most dangerous misconceptions about alcohol. It also runs in reverse: the adaptation eases when the drinking stops, which is why people who take a month off — going sober for October, say — often find the same two drinks land harder in November. If you are counting those days rather than estimating a number, the sobriety counter counts them from the date of your last drink.

Body composition: Muscle tissue contains more water than fat tissue. At the same weight, someone with more muscle mass will generally have a lower BAC because alcohol distributes through water in the body.

BAC in per cent, promille and grams per litre

0.08% BAC is about 0.8 per mille (0.8‰), or 0.8 grams of alcohol per litre of blood. A per-cent BAC counts grams per 100 ml and the other two count per 1,000 ml, so converting is a matter of moving the decimal point one place: 0.05% is 0.5‰ and 0.02% is 0.2‰.

Germany, Austria, the Netherlands, Poland and the Nordic countries write their limits in promille; France, Italy, Spain and Portugal write the same number as grams per litre, and Japan’s road-traffic law uses milligrams per millilitre. Strictly, promille is measured per kilogram of blood, which is slightly heavier than water, so 0.08% is nearer 0.76‰ — the table uses the rounding everyone else does.

BAC (%) Promille (‰) Grams per litre (g/l)
0.02% 0.2 ‰ 0.2 g/l
0.03% 0.3 ‰ 0.3 g/l
0.05% 0.5 ‰ 0.5 g/l
0.08% 0.8 ‰ 0.8 g/l
0.10% 1.0 ‰ 1.0 g/l
0.15% 1.5 ‰ 1.5 g/l
0.20% 2.0 ‰ 2.0 g/l

BAC and Driving

In the United States, the legal limit for drivers 21 and over is 0.08% BAC in all 50 states. For commercial drivers it’s 0.04%, and for drivers under 21, most states enforce zero-tolerance policies (0.00–0.02%).

International limits vary significantly. Many European countries set the limit at 0.05%, while countries like Sweden, Poland, and Norway use 0.02%. Some countries — including the Czech Republic, Hungary, and several Middle Eastern nations — enforce a strict 0.00% limit.

Impairment begins well below the legal limit. Studies show that reaction time and divided attention are measurably impaired at BAC levels as low as 0.02%. At 0.05%, the risk of a crash is roughly double that of a sober driver.

The safest choice is always to not drive after drinking. Use a rideshare, call a cab, or designate a sober driver. No estimate can guarantee you are safe to drive. That holds the next day too, which is where most people underestimate the arithmetic — the morning after calculator runs the same sum forward from the hour you stopped and prints it as a clock time rather than a countdown.

Asked and answered

Frequently Asked Questions

How accurate is a BAC calculator?
BAC calculators use the Widmark formula, which provides a reasonable estimate. However, actual BAC varies based on genetics, liver function, food intake, medications, and other factors. This is an estimate — not a breathalyzer.
What BAC level is legally drunk?
In most US states, the legal limit is 0.08%. However, impairment begins well below that level. Many countries use lower limits (0.05% or even 0.02%).
How long does it take to sober up?
Your body eliminates alcohol at approximately 0.015% BAC per hour (roughly one standard drink per hour). Nothing speeds this up — not coffee, cold showers, or food. Only time works.
Why does weight affect BAC?
Alcohol distributes through body water. Larger people have more body water to dilute the alcohol, resulting in a lower BAC from the same number of drinks.
How long does it take for BAC to go down?
At the average rate, BAC falls about 0.015% an hour from its peak, roughly one US standard drink an hour. A peak of 0.08 takes a little over five hours to reach zero. The curve on this page draws that fall hour by hour from your own numbers, and nothing speeds it up.
What is 0.08 BAC in promille?
0.08% BAC is about 0.8 per mille (0.8‰), or 0.8 grams of alcohol per litre of blood. Move the decimal point one place to the right: 0.05% is 0.5‰ and 0.02% is 0.2‰. Germany, Poland, the Netherlands and the Nordic countries write limits in promille; France, Italy and Spain write the same number as grams per litre.
How do I read the BAC by weight chart?
Find your weight in the first column and the number of standard drinks along the top. The cell is the estimated peak if those drinks landed together. Subtract about 0.015 for every hour since your first drink. The same drinks give a woman a higher BAC than a man of the same weight, so each has a chart of their own.

Drink Driving Limit

The legal limit where you are and how long alcohol stays measurable. Never a permission to drive.

Alcohol Units Calculator

Any drink turned into your country's units, with the standard drink and the guideline of 23 countries side by side.

Alcohol Calories Calculator

The calories in what you drank, shown beside the food you would have to eat to match them.

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