EDUCATIONAL TOOL — NOT MEDICAL ADVICE Standard drink defined per NIAAA (14g pure alcohol). Legal limits vary by jurisdiction — always check local law.

Free Tool

BAC & Standard Drink Calculator

Standard drinks vs. limits — pick what you're drinking and see your estimated BAC against common legal limits.

What are you drinking? Number of Servings

= Standard Drinks

Hours Spent Drinking

Body Weight

Biological Sex

Driver Under 21 (Zero Tolerance — 0.02%) Commercial Driver (CDL — 0.04%)

🚗 Enter your details to see your estimated BAC.

Estimated BAC

0.000%

Against Common Legal Limits

Blood Alcohol Calculator Over Time: How BAC Changes Hour by Hour

Wine glass and car keys with a clock showing blood alcohol changing hour by hour

Legal-limit math is a snapshot. A blood alcohol calculator over time asks how that snapshot decays. After peak, this site’s teaching slope is about 0.015% BAC per hour (same Widmark-style elimination as Time to Sober).

Worked example (170 lb male, 4 NIAAA drinks, 2 hours)

Peak ≈ 0.092%. At a 0.08% US adult limit the model is still over at hour 0 and crosses under around hour 1 after peak. At 0.05% it takes until about hour 3. At 0.00% about hour 7. None of those hours is permission to drive.

Hours after peak	Estimated BAC	vs 0.08%
0	0.092%	Over
1	0.077%	Under 0.08% in the model — still impaired
2	0.062%	Under
4	0.032%	Under
6	0.002%	Near zero

Estimated BAC vs hours after peak (0.015%/hour; educational, not a driving pass)

Use the drink picker above for standard-drink counts, then the countdown tool for the hour-by-hour curve. Pillar context: alcohol detection windows.