What this alcohol reading calculator estimates
This calculator provides an estimated blood alcohol concentration (BAC) and an approximate breath alcohol reading (BrAC). It uses your drink amount, alcohol strength, body weight, time since drinking began, and Widmark distribution factors to model how alcohol is likely distributed and metabolized in the body.
You will see several outputs:
- BAC (%) — grams of alcohol per 100 mL of blood.
- BrAC (mg/L) — estimated breath reading based on a common blood-to-breath ratio.
- Promille (‰) — BAC expressed per thousand.
- Time to 0.00% — a rough estimate of additional hours for BAC to approach zero.
How the estimate works
1) Pure alcohol intake
The calculator first estimates total ethanol consumed:
grams of ethanol = number of drinks × drink volume × (ABV/100) × 0.789
Here, 0.789 is ethanol density in g/mL.
2) Distribution in body water
Alcohol distributes through body water rather than total body mass. Widmark factors are used to approximate this:
- Male: 0.68
- Female: 0.55
- Other estimate: 0.615
The tool applies these factors to estimate initial BAC before metabolism.
3) Metabolic elimination over time
A commonly used elimination rate of 0.015% BAC per hour is then subtracted from the estimate. This reflects average metabolism, but real rates can differ meaningfully between individuals.
How to use this calculator correctly
- Enter realistic drink volume and ABV. Craft beer, wine, and spirits can vary a lot.
- Use your actual body weight and correct unit (kg or lb).
- Set hours since your first drink, not just your most recent one.
- Interpret results as a range, not an exact measurement.
Reading interpretation guide
Typical effect zones (approximate)
- 0.00%–0.019%: Minimal measurable impairment.
- 0.02%–0.049%: Mild relaxation; reduced divided attention possible.
- 0.05%–0.079%: Noticeable impairment in reaction time and coordination.
- 0.08%–0.149%: Significant impairment; often at/over legal driving limits in many regions.
- 0.15%+: Major impairment and elevated risk of alcohol poisoning.
Factors that can shift your real alcohol reading
- Food intake: Drinking on an empty stomach can spike BAC faster.
- Drinking pace: Rapid intake produces higher peaks.
- Body composition: Same weight does not equal same body-water percentage.
- Medication interactions: Some drugs amplify alcohol effects or alter metabolism.
- Sleep deprivation and illness: Can worsen impairment even at lower BAC levels.
- Measurement differences: Breath devices vary by calibration, environment, and technique.
Safety first
If you have consumed alcohol, assume you may be impaired longer than expected. Plan transportation in advance, use a designated driver or rideshare, and avoid operating vehicles or hazardous equipment after drinking. If someone shows signs of severe intoxication (confusion, vomiting, slow breathing, unconsciousness), seek emergency medical help immediately.
Quick FAQ
Can this replace a police or clinical breathalyzer?
No. This is an educational estimator, not a certified instrument.
Does coffee, water, or a cold shower lower BAC quickly?
No. These may change how alert someone feels, but they do not significantly accelerate alcohol metabolism.
Why is my calculated value different from how I feel?
Perceived impairment varies widely. Tolerance can mask feelings without reducing actual risk.