Blood Alcohol Calculator (BAC)
Estimate blood alcohol concentration with the Widmark formula.
Quick answer
- Formula: Widmark: BAC% = alcohol (g) ÷ (weight (kg) × r × 10) − 0.015 × hours, floored at 0 (r = 0.68 men, 0.55 women)
- Worked example — Estimated BAC: 0.088% (full example below).
Blood Alcohol Calculator (BAC)
| Estimated BAC | 0.088% |
| Pure alcohol consumed | 56 g |
Four standard drinks (56 g of alcohol) in an 80 kg man give a Widmark BAC of about 0.088% after one hour — above the 0.08% driving limit used in most of the US.
The Widmark formula, developed in the 1930s and still used in forensic toxicology, estimates blood alcohol concentration from the pure alcohol consumed, body weight and a distribution factor (r = 0.68 for men, 0.55 for women, reflecting body-water share). This calculator counts one US standard drink as 14 grams of pure alcohol — roughly a 355 ml beer at 5%, 150 ml wine at 12%, or 44 ml spirits at 40% — and subtracts elimination at 0.015% per hour.
BAC estimates are rough: food, medications, pour sizes and individual metabolism shift real values widely, and any amount of alcohol impairs driving. Never use this calculator to decide you are safe to drive — if you have been drinking, do not drive. Educational information only, not medical or legal advice.
The formula
Worked example
Four standard drinks (56 g of alcohol) in an 80 kg man give a Widmark BAC of about 0.088% after one hour — above the 0.08% driving limit used in most of the US.
The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.
Frequently asked questions
Why do women reach a higher BAC from the same drinks?
The distribution factor r is lower (0.55 vs 0.68) because women on average carry a higher share of body fat and less body water, so the same alcohol dose concentrates in a smaller fluid volume.
How fast does BAC fall?
The liver eliminates alcohol at a roughly constant rate, modelled here as 0.015% per hour (observed range about 0.010–0.020). Coffee, food after the fact and fresh air do not speed it up — only time does.
What is the legal driving limit?
0.08% in most US states (0.05% in Utah), 0.05% in most of Europe and Australia, and lower or zero for novice and commercial drivers in many places. Impairment begins well below any limit.
Category: Health & Fitness calculators
Sources & methodology
This calculator applies the formula shown on this page exactly as written, using the standard definitions for its inputs. Results are computed from the values you enter — no data is stored — and are rounded only for display.
Content last reviewed by CalcHub Editorial.
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