Blood Alcohol (BAC) Calculator
An estimated blood alcohol concentration from your standard drinks, hours and body weight, with the time until you are under 0.05 and back to zero.
Peak BAC = (drinks × grams per drink) ÷ (body weight in grams × r) × 100, where r is the Widmark body-water factor (0.
How the blood alcohol (bac) calculator works
Peak BAC = (drinks × grams per drink) ÷ (body weight in grams × r) × 100, where r is the Widmark body-water factor (0.68 for men, 0.55 for women). The body clears about 0.015 % an hour, so BAC now is the peak less 0.015 × hours since the first drink. Time to a limit is the BAC above it divided by 0.015.
Formula: Peak % = drinks × g ÷ (weight kg × 1000 × r) × 100 · BAC now = peak − 0.015 × hours · hours to 0.00 = BAC ÷ 0.015
How the BAC estimate is worked out
The Widmark equation
The calculator uses the classic Widmark equation. It takes the grams of alcohol you have consumed — the number of standard drinks × 10 g for Australia — and divides by your body weight in grams multiplied by a distribution factor (about 0.68 for men and 0.55 for women, because women on average carry less body water). It then subtracts the alcohol your body has already cleared, at roughly 0.015% of BAC per hour — about one standard drink an hour. The result is your estimated blood alcohol concentration as a percentage.
A standard drink is often less than a glass
An Australian standard drink is 10 g of pure alcohol, which is frequently less than a full glass. A 150 ml glass of wine is about 1.5 standard drinks, a full-strength schooner (425 ml) about 1.6, and a middy of full-strength beer about 1.1. Home pours are usually bigger than a standard drink, so it is easy to underestimate — when unsure, assume you have had more.
Worked example
An 80 kg man having 4 standard drinks over 2 hours: 4 × 10 g = 40 g of alcohol, giving a starting BAC of about 0.073%, less roughly 0.03% cleared over 2 hours ≈ 0.043% — under 0.05 but marginal, and easily over with a slightly bigger pour or less time. A 60 kg woman having the same four drinks over the same two hours works out to about 0.09% — well over the limit. Same drinks, very different result.
This is a rough estimate only. It is not a breathalyser, not a legal defence, and your real BAC can be much higher. After drinking, the only safe choice is not to drive — arrange a lift, taxi, rideshare or public transport.
Standard drinksWhat counts as a standard drink in Australia
Because the calculator works in standard drinks, counting them accurately is what makes or breaks the estimate. In Australia one standard drink is 10 g of pure alcohol — and that is usually smaller than the glass in your hand.
- 150 ml glass of wine (13%) ≈ 1.5 standard drinks.
- Full-strength schooner, 425 ml (4.8%) ≈ 1.6 standard drinks.
- Middy of full-strength beer, 285 ml ≈ 1.1 standard drinks.
- 30 ml nip of spirits (40%) = 1 standard drink.
- A bottle of wine holds around 7–8 standard drinks.
Poured at home, a "glass" of wine or a spirit mixer is often much larger than a standard drink, so it is easy to have far more than you counted. When in doubt, round up — and remember the estimate assumes each drink is exactly one standard drink at the strength you enter.
Limits, sobering up & safetyAustralian limits, sobering up and staying safe
The drink-driving limits
For a full (open) licence the legal limit is a BAC under 0.05. A zero limit of 0.00 applies to learner and provisional (P-plate) drivers, and to drivers of heavy vehicles, public passenger vehicles and dangerous-goods vehicles. Going over means heavy fines, licence loss and, for higher readings or repeat offences, criminal charges. An estimate under 0.05 here is not permission to drive.
Only time sobers you up
Your body clears alcohol at about 0.015% of BAC per hour — roughly one standard drink an hour — and you cannot speed it up. Coffee, water, food, a cold shower and fresh air do not lower your BAC; only time does. After a heavy night you can still be over the limit the next morning.
The only safe choice
This tool is for general education only. It is not a breathalyser, it is not a legal defence, and real BAC readings are often higher than an estimate. If you have had any alcohol, plan not to drive at all — book a taxi or rideshare, catch public transport, arrange a lift, or stay put. It is never worth the risk to yourself or anyone else on the road.
Frequently asked Frequently asked questions
Where these figures come from
The method reflects the widely used Widmark model and standard Australian drink and drink-driving definitions. Individual results vary considerably, so treat every number as a rough planning figure rather than a measurement.
- Standard drink — 10 g of pure alcohol, the Australian definition used across health guidance and labelling.
- Widmark distribution factor — approximately 0.68 for men and 0.55 for women, reflecting average body-water differences.
- Alcohol clearance — about 0.015% of BAC per hour on average, roughly one standard drink an hour; only time reduces BAC.
- Drink-driving limits — under 0.05 for a full licence; 0.00 for learner, provisional, heavy-vehicle, public-passenger and dangerous-goods drivers.
- Further guidance — healthdirect — Australian government health advice.
Last checked: July 2026. This is a general educational estimate, not medical or legal advice, and not a breathalyser reading. Real BAC can be much higher than shown. The safest choice after drinking is always not to drive.
Understanding your resultSelect the question that matches where you are right now.
The headline number is your estimated blood alcohol concentration as a percentage, from the Widmark equation. The breakdown shows the alcohol consumed, the amount your body has cleared over time, and how weight and sex shaped the result.
What to do with itUse it only to understand how quickly drinks add up and how slowly alcohol leaves. It is educational — it is not a signal that you are safe to drive at any reading.
What it is notIt is not a breathalyser, not a legal defence and not medical advice. Your real BAC can be much higher, and only a police test measures it for the law.
The safe choiceAfter any drinking, plan not to drive. Book a taxi or rideshare, catch public transport, arrange a lift, or stay the night.
Four things move your estimated BAC the most: how many standard drinks you have had, your body weight, your sex, and the time since your first drink.
Drinks & strengthEach standard drink adds 10 g of alcohol. Larger home pours mean more standard drinks than you may realise, pushing BAC up fast.
Weight & sexAlcohol spreads through body water. A lighter person, and on average a woman, reaches a higher BAC from the same drinks.
TimeYour body clears about 0.015% per hour, so BAC falls slowly. You can still be over the limit hours later — even the next morning.
There is no trick to lower your BAC quickly — but there are simple ways to stay safe.
Plan your ride firstDecide how you are getting home before you start drinking — a taxi, rideshare, public transport or a sober driver.
Count your drinksTrack standard drinks, not glasses, and remember home pours are usually larger. When unsure, assume you have had more.
Give it timeOnly time lowers BAC. If in any doubt the next day, do not drive — you may still be over the limit.
Your health and habits add up in other ways too. Explore these related calculators.
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Cost of smoking calculator → Daily energyAlcohol has calories too — check your needs.
Calorie calculator → Getting your licenceBudget your learner driving lessons.
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What is a standard drink in Australia? 10 g of pure alcohol
An Australian standard drink contains 10 grams of pure alcohol — the amount a healthy liver clears in about an hour. Crucially, it's often less than a full serve: a 375 ml mid-strength beer is about 1, a 375 ml full-strength beer about 1.4, a restaurant glass of wine (150 ml) about 1.5, and a 30 ml nip of spirits about 1. So 'four drinks' on a night out is frequently five or six standard drinks. Count standard drinks, not glasses.
| Standard drink | 10 g alcohol |
|---|---|
| Glass of wine | ~1.5 std |
| Full-strength schooner | ~1.6 std |
- Count Standard drinks
- Not Glasses
Example: 80 kg man, 4 drinks, 2 hours ≈ 0.043 — under 0.05
Using the Widmark formula, an 80 kg man who has 4 standard drinks over 2 hours has an estimated BAC of about 0.043 — under the 0.05 full-licence limit, but not by much. It would take roughly 3 hours from then to reach zero. That's an average, though: drink the same amount faster, on an empty stomach, or if you're smaller, and you could easily be over 0.05. The margin is thin enough that the safe call is not to drive.
| BAC | ≈0.043 |
|---|---|
| Limit | 0.05 |
| To sober | ~3 hours |
- Thin margin Easily tipped over
- Safe call Don't drive
Why the same drinks hit women harder Higher BAC per drink
For the same weight and drinks, women typically reach a higher BAC than men, because the body-water constant is lower (about 0.55 vs 0.68) — alcohol distributes into less body water. A 60 kg woman having 4 standard drinks over 2 hours has an estimated BAC around 0.09, well over 0.05, versus ~0.043 for an 80 kg man. Body size and sex both matter, which is why 'how many drinks is okay' has no universal answer.
| 60 kg woman, 4 drinks | ≈0.09 |
|---|---|
| 80 kg man, 4 drinks | ≈0.043 |
| Reason | Less body water |
- Same drinks Higher BAC
- No universal 'safe' number
The AU drink-driving limits 0.05 full · 0.00 L/P
In Australia the general limit for a full licence holder is a BAC under 0.05. Learner and provisional (P-plate) drivers must be at 0.00 — zero — and so must drivers of trucks, buses, taxis and other special vehicles. Penalties start at a fine and licence loss and rise steeply with BAC and repeat offences. Because BAC is hard to judge from how you feel, the only reliable way to stay under a limit is to not drink if you're driving.
| Full licence | Under 0.05 |
|---|---|
| Learner / P | 0.00 |
| Heavy vehicles | 0.00 |
- L / P plates Zero tolerance
- Driving? Don't drink
How long until I'm sober? ~1 standard drink per hour
Your body clears alcohol at a roughly fixed rate — about 0.015% BAC, or one standard drink, per hour — and nothing speeds it up. From a BAC of 0.043 it takes about 3 hours to reach zero; from 0.09, about 6 hours. That's why you can be over the limit the morning after a big night. Coffee, a cold shower, water, food, exercise and fresh air make you feel more alert but do not lower your BAC. Only time does.
| Clearance | ~0.015%/hr |
|---|---|
| From 0.043 | ~3 hrs to zero |
| Coffee/shower | Do nothing |
- Morning after Can still be over
- Only time Sobers you
How accurate is a BAC estimate? Rough — treat as indicative
The Widmark formula is a population average and can be off by a wide margin for any individual. Food in your stomach slows absorption; drinking fast spikes it; body composition, liver health, medications, hydration and even genetics all shift the result. It also can't know exactly how much you drank. Treat any BAC calculator as indicative only, never as a green light to drive — and if there's any doubt at all, don't.
| It's a | Population average |
|---|---|
| Affected by | Food, speed, meds |
| Never | A driving green light |
- Could be Higher than shown
- Any doubt Don't drive
Worked examples
| Inputs | Estimated BAC now | Note |
|---|---|---|
| 4 standard drinks over 2 hours, 80 kg man | 0.044% | about 0.044 %, sober in 2 h 54 min |
| 2 drinks over 1 hour, 60 kg woman | 0.046% | about 0.046 % |
| Nothing to drink | 0% | 0.000 % |
FAQFrequently asked questions
How is blood alcohol concentration calculated?
This calculator uses the Widmark equation. It takes the grams of alcohol you have consumed (standard drinks × 10 g in Australia), divides by your body weight in grams multiplied by a distribution factor (about 0.68 for men and 0.55 for women), then subtracts the alcohol your body has cleared over time at roughly 0.015% per hour. The result is an estimated blood alcohol concentration as a percentage. It is only an estimate: it cannot know your exact body composition, what you have eaten, your metabolism or how strong each drink really was, so your real BAC can be higher. It is never a legal defence and should never be used to decide whether to drive.
What is a standard drink in Australia?
An Australian standard drink contains 10 grams of pure alcohol. That is often much less than a full glass: a 150 ml glass of wine is about 1.5 standard drinks, a full-strength schooner (425 ml) is about 1.6, a middy (285 ml) of full-strength beer is about 1.1, and a 30 ml nip of spirits is 1. Drinks poured at home are frequently larger than a standard drink, so it is easy to have more than you think. Because the calculator works in standard drinks, counting them accurately matters — and when in doubt, assume you have had more.
How long does it take to sober up?
Your body clears alcohol at roughly 0.015% of BAC per hour, which works out to about one standard drink an hour — and you cannot speed it up. Coffee, water, food, a cold shower and fresh air do not lower your BAC; only time does. As a rough guide, someone at 0.05% would take around three to four hours to reach zero, and much longer after a heavy night, meaning you can still be over the limit the next morning. If you have been drinking, plan not to drive at all — arrange a lift, taxi, rideshare or public transport.
What is the drink-driving limit in Australia?
For a full (open) licence the legal limit is a BAC under 0.05%. A zero limit of 0.00% applies to learner and provisional (P-plate) drivers, and to drivers of heavy vehicles, public passenger vehicles and dangerous-goods vehicles. Penalties for exceeding the limit include heavy fines, licence loss and, for higher readings or repeat offences, criminal charges. The safest approach is simple: if you have had any alcohol, do not drive. A calculator estimate under 0.05% is not permission to get behind the wheel.
How accurate is a BAC calculator?
Not accurate enough to rely on. The Widmark equation is a population average and cannot account for your individual metabolism, body composition, hydration, food intake, medications, health conditions or the true strength of each drink. Real BAC readings often differ from an estimate, and frequently come out higher. This tool is for general education only — it is not a breathalyser, not a legal defence, and not a way to check whether you are safe to drive. After drinking, the only safe choice is not to drive. Sources
The sources behind this calculator
- Mifflin MD et al., "A new predictive equation for resting energy expenditure in healthy individuals", Am J Clin Nutr 1990 — the BMR equation used here
- World Health Organization — Waist circumference and waist–hip ratio (2008 expert consultation) — waist-to-hip cut-offs
- Tanaka H, Monahan KD, Seals DR, "Age-predicted maximal heart rate revisited", J Am Coll Cardiol 2001 — 208 − 0.7 × age
- Nathan DM et al., "Translating the A1C assay into estimated average glucose values" (ADAG), Diabetes Care 2008 — eAG = 28.7 × A1c − 46.7
- Mosteller RD, "Simplified calculation of body-surface area", N Engl J Med 1987 — BSA = √(height × weight / 3600)
- Australian Department of Health and Aged Care — national health guidance
Last checked: July 2026. The equations are fixed by their published papers and do not change with tax years or regulations; the thresholds quoted in verdicts name the body that set them.