BAC Calculator

Check your estimated blood alcohol concentration in about ten seconds: four quick questions, no account, no name, no personal details. You’ll get your estimated BAC, what it means in plain language, and the number people actually come here for — when you’ll be back to 0.00.

This tool is built by Think Twice, a nonprofit dedicated to preventing impaired driving. It always shows you the cautious estimate, and it will never tell you you’re “fine to drive.”

Think Twice · Free safety tool

BAC Calculator

Estimate your blood alcohol concentration — and when you’ll be back to 0.00.

Checking on:
1 · Sex

The formula only has data for male/female bodies — pick the closer one.

2 · Weight
lb
3 · What you've had
Beer12 oz · 5% — 1 standard drink 0
Wine5 oz · 12% — 1 standard drink 0
Shot / cocktail1.5 oz · 40% — 1 standard drink 0

Tall or strong pours count as more — a 16 oz, 7% IPA ≈ 1.9 drinks. Doubles = 2.

4 · Time since your first drink
Shared estimate — not yours.
Tap your details — takes 10 seconds.

Your estimate appears here instantly. Nothing is required, nothing is stored.

0.000%
 

 

Back to 0.00 —  
You counted —  

Only time gets you to 0.00 — not coffee, food, water, or a cold shower.

Heads up: alcohol takes 30–90 minutes to fully absorb — this number may still be climbing.
At this level people can lose consciousness. Stay with them. If they can't be woken, breathe slowly or irregularly, or vomit while passed out — call 911 now.
No chart replaces observation. Slurred speech, glassy eyes, loud-then-slow talk — when in doubt, slow the service, bring water, and don't let them drive.

No amount of alcohol is safe to drive on. Whatever this estimate says — even a number under a legal limit — the only safe BAC for driving is 0.00.

0.08 DUI, all states 0.05 Utah 0.04 Commercial Any Under 21

Legal limits are reference points, not safety lines — impairment starts below all of them.

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While you're watching your number, watch your drink. Drink spiking is real — test strips detect GHB & ketamine in seconds. Ask your bar if they stock them, or keep a pack on you. Drink Spike Test Strips →

This is an educational estimate, not a measurement. Real BAC varies with health, medications, food, and drink strength. Never use it to decide whether to drive.

How this is calculated (and the full disclaimer)

Widmark formula, cautious variant: %BAC = drinks×14g ÷ (weight×r) × 100 − 0.015 × (hours − 0.5) with r = 0.68 (male) / 0.55 (female), elimination 0.015%/hour (real range ≈ 0.010–0.025), no elimination credit for the first 30 minutes, never below zero. Standard drink = 14 g alcohol (NIAAA): 12 oz 5% beer = 5 oz 12% wine = 1.5 oz 40% spirits. Crash-risk figures: NHTSA case-control study (2015). We deliberately show the cautious end of the range.

This calculator is provided by Think Twice for education only. Individual results vary widely with metabolism, health conditions, medications, food, and drink strength, and can differ from this estimate by a large margin in either direction. Alcohol can also keep being absorbed after you stop drinking, so your real BAC may still be rising. It is not medical or legal advice, not a breath or blood test, and not an administered or evidentiary test — it is not admissible in any legal proceeding. The consumption of any amount of alcohol can impair your ability to drive safely, regardless of what this or any other test result says: no result, including one below a legal limit, means it is safe or lawful for you or anyone else to drive or operate equipment. The only safe BAC for driving is 0.00. If you've been drinking, arrange a ride or wait until you're fully sober. If someone may have alcohol poisoning (unresponsive, slow or irregular breathing, vomiting while passed out), call 911. This tool is intended for people over the age of 21. It does not account for interactions with prescription, over-the-counter, or illegal drugs.

Your use of this tool is also governed by our Terms of Service and Privacy Policy.

How this calculator works

We use the Widmark formula — the same math used in forensic BAC estimation — with deliberately cautious settings: classic Widmark body-water factors (0.68 male / 0.55 female), an average elimination rate of 0.015% per hour, and no elimination credit for the first 30 minutes while alcohol is still absorbing. One “standard drink” means 14 grams of alcohol (NIAAA): a 12 oz beer at 5%, a 5 oz glass of wine at 12%, or a 1.5 oz shot at 40% are all one drink. Crash-risk context comes from NHTSA’s case-control crash study. Full details and the complete disclaimer are inside the calculator under “How this is calculated.”

How long does alcohol stay in your system?

Your body clears roughly 0.015% BAC per hour — about one standard drink an hour — and nothing speeds that up. Not coffee, not food after the fact, not water, not a cold shower. Time is the only thing that lowers BAC, which is why this calculator’s most important output isn’t your number now, it’s the estimate of when you’ll be back to 0.00.

Is there a “safe” BAC for driving?

Impairment starts well below the legal limit — judgment and reaction time are measurably affected in the 0.02–0.05 range, and at 0.05 crash risk has roughly doubled. 0.08% is a DUI in every US state (0.05% in Utah, 0.04% for commercial drivers, and any amount under 21). Legal and safe are not the same thing: the only BAC this tool will ever call safe for driving is 0.00. If you’ve been drinking, don’t drive — get a ride.

Serving guests?

Bartenders and venue staff: switch the calculator to “A guest (I’m serving)” for third-person estimates and service guidance. Numbers help, but no chart replaces observation — when in doubt, slow the service and don’t let them drive.