Blood Alcohol Calculator
Estimate blood alcohol concentration with the Widmark formula from drinks, body weight, sex and hours elapsed, plus time until zero. Never a reason to drive.
Blood Alcohol Calculator: with the default inputs, estimated bac now is 0.053%.
Widmark's distribution ratio: the share of body weight that is water.
Count servings of the size and strength below.
12 fl oz beer · 5 fl oz wine · 1.5 fl oz spirits.
Beer ~5%, wine ~12%, spirits ~40%.
Used only in 'grams' mode. One US standard drink is 14 g.
Grams of alcohol per 100 mL of blood, as a percentage.
- Peak BAC (no elimination)
- 0.083%
- Time until below 0.08%
- Already below 0.08% (still impaired)
- Time until 0.00%
- 3 h 30 min
- Alcohol consumed
- 42grams of pure ethanol
- US standard drinks
- 314 g of alcohol each.
Assumptions
- Widmark formula with r = 0.68 (men) / 0.55 (women) and elimination β = 0.015% per hour; both vary widely between individuals.
- All alcohol is assumed absorbed at time zero. Real BAC peaks 30–90 minutes after the last drink.
- Ethanol density 0.789 g/mL; US standard drink 14 g.
- For education only. Never use this to decide whether to drive, operate machinery, or whether someone needs medical help.
| Hours since first drink | BAC | |
|---|---|---|
| 0 | 0.083% | over 0.08 |
| 1 | 0.068% | over 0.05 |
| 2 | 0.053% | over 0.05 |
| 3 | 0.038% | |
| 4 | 0.023% | |
| 5 | 0.008% | |
| 6 | 0% | sober |
How this is worked out
The formula
Widmark: BAC % = (A ÷ (r × W)) × 100 − β × t A = grams of alcohol = volume (mL) × ABV × 0.789 g/mL W = body weight in grams r = distribution ratio: 0.68 men, 0.55 women β = elimination rate, 0.015 % per hour t = hours since drinking began
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Body weight
- A number.in lb, kg, st · from 60 to 700 · defaults to 165
- Sex
- Widmark's distribution ratio: the share of body weight that is water.Male (r = 0.68) · Female (r = 0.55)
- Enter alcohol as
- Choose one of 2 options.Number of drinks × size × strength · Grams of pure alcohol
- Drinks
- Count servings of the size and strength below.from 0 to 40 · defaults to 3
- Serving size
- 12 fl oz beer · 5 fl oz wine · 1.5 fl oz spirits.in fl oz, mL · from 0 to 100 · defaults to 12
- Alcohol by volume
- Beer ~5%, wine ~12%, spirits ~40%.a percentage · from 0 to 96 · defaults to 5
- Grams of alcohol
- Used only in 'grams' mode. One US standard drink is 14 g.from 0 to 600 · defaults to 42
- Hours since first drink
- A number.from 0 to 48 · defaults to 2
What you get back
- Estimated BAC nowmain answer
- Grams of alcohol per 100 mL of blood, as a percentage.
- Peak BAC (no elimination)
- Time until below 0.08%
- Time until 0.00%
- Alcohol consumed
- grams of pure ethanol
- US standard drinks
- 14 g of alcohol each.
What this assumes
- Widmark formula with r = 0.68 (men) / 0.55 (women) and elimination β = 0.015% per hour; both vary widely between individuals.
- All alcohol is assumed absorbed at time zero. Real BAC peaks 30–90 minutes after the last drink.
- Ethanol density 0.789 g/mL; US standard drink 14 g.
- For education only. Never use this to decide whether to drive, operate machinery, or whether someone needs medical help.
About this calculator
Blood alcohol concentration is the mass of alcohol per volume of blood, written as a percentage: 0.08% means 80 mg per 100 mL. This calculator uses the Widmark formula — the equation forensic toxicologists have used since the 1930s — to estimate where you are now and how long until you're clear. It is an estimate of a population average, and the individual error is large. Read the warnings; they aren't boilerplate.
How Widmark works
Alcohol distributes into body water, not fat. Widmark's r factor (0.68 for men, 0.55 for women) is the share of body weight that behaves like water, so a given dose produces a higher concentration in a smaller or higher-body-fat person. The body then removes alcohol at a fairly constant rate — about 0.015% per hour, roughly one standard drink an hour — regardless of coffee, cold showers or exercise.
A US standard drink is 14 g of alcohol: 12 fl oz of 5% beer, 5 fl oz of 12% wine, 1.5 fl oz of 40% spirits. Real pours and craft beers are often much larger; enter the actual size and strength.
What the results mean
- 0.02–0.05%: relaxed, mild judgment and coordination changes. Crash risk is already elevated.
- 0.05%: the per se limit in Utah and most of Europe; impairment is measurable.
- 0.08%: the per se limit in the other 49 US states. Reaction time and tracking are clearly impaired.
- 0.15–0.20%: gross motor impairment, vomiting, blackouts.
- 0.30%+: risk of unconsciousness and respiratory depression — a medical emergency.
The "time until 0.08%" and "time until zero" lines simply divide by the elimination rate. They tell you the arithmetic, not whether you're safe.
Why your real BAC may differ
- Absorption isn't instant. BAC keeps rising for 30–90 minutes after the last drink, longer on a full stomach. The formula assumes everything was absorbed at time zero.
- r varies widely — from about 0.55 to 0.85 in men and 0.45 to 0.70 in women — with age, body composition and fitness. That alone is ±20%.
- Elimination ranges from 0.010 to 0.025%/h; heavy drinkers metabolise faster, some people slower.
- Medications, liver disease, and drinking on an empty stomach all shift the result.
The only rule that matters
A calculator cannot tell you whether you're fit to drive. Impairment begins with the first drink, breathalysers and blood tests measure what the formula only guesses, and being "under the limit" is not a defence against a charge of impaired driving. If you've been drinking, don't drive. Plan the ride home before the first drink.
Frequently asked questions
▸How long does it take to sober up?
About one standard drink per hour — 0.015% BAC per hour on average. From 0.08% that's roughly 5–6 hours to zero. Coffee, food and exercise don't speed it up.
▸How many drinks is 0.08%?
For a 165-lb man about 4 standard drinks in an hour; for a 130-lb woman about 2–3. Larger pours and stronger drinks get you there faster, and individual variation is large.
▸Is this calculator accurate enough to decide if I can drive?
No. The Widmark estimate can be off by 0.02% or more either way, absorption timing adds more uncertainty, and impairment starts below any legal limit. If you've been drinking, don't drive.
▸Why do women get a higher BAC from the same drinks?
On average women have a lower proportion of body water (Widmark r of 0.55 vs 0.68), so the same alcohol is concentrated in less fluid. Lower gastric alcohol dehydrogenase activity also plays a role.
▸What counts as one standard drink?
In the US, 14 g of pure alcohol: a 12-oz 5% beer, 5 oz of 12% wine, or 1.5 oz of 80-proof spirits. A pint of 7% IPA is about 1.9 standard drinks.
Put this calculator on your own site
A working bac, free for any site, with no ads and no sign-up. It resizes to fit wherever you paste it and updates itself as this page improves.
Paste this anywhere. It works on any site, carries no ads, never expires, and always shows the current version.
Blood Alcohol Calculator by CalculateItNow
The page's own title. The clearest description of what the link leads to.
The credit line sits outside the widget on purpose, so it is a real link on your page rather than one buried in a frame. Please keep it — it is what pays for CalculateItNow staying free and ad-free. The script only resizes the widget to fit its contents; drop it and the widget still works.
Browse every calculator widget·How to add it to WordPress, Squarespace or Wix
Related calculators
The questions people ask next to a bac.
Calculate your body mass index from height and weight, see your category, and find the weight range that counts as healthy for your height.
Estimate how much water to drink a day from body weight, exercise and climate, compared with the NASEM adequate intake — and an honest take on the '8 glasses' rule.
Find how many calories a day to eat to maintain, lose or gain weight, with BMR and TDEE shown, Mifflin-St Jeor by default, and warnings if the target is too low.
Convert pounds, ounces, stone, kilograms, grams, milligrams and tons in one go using the exact 1959 definitions — with a body-weight table and cooking equivalents.
Count the days, weeks, months and business days between two dates, or add and subtract days, weeks, months or years from any date — leap years handled exactly.