OmniTools

Blood Alcohol (BAC) Calculator

Estimate blood alcohol with the Widmark formula. An estimate only — never a fitness-to-drive test.

Basis: Widmark: BAC (%) = grams of alcohol ÷ (body weight in grams × r) × 100, with r = 0.68 for men and 0.55 for women; ethanol density 0.789 g/mL and elimination of 0.015 percentage points per hour·2026-09-13 verified·Not reviewed by a medical professional·Editorial policy

Before you rely on this

Do not use this to judge fitness to drive. Widmark estimates scatter widely between people of the same weight drinking the same thing, and an empty stomach, medication, liver function and fatigue move the real figure in ways the formula cannot follow. The 0.015%-per-hour elimination rate is likewise an average.

Tool Overview & Key Purpose

Estimates blood alcohol with the Widmark formula and shows how it falls as the body eliminates it. It does not hide how wide the spread on such an estimate is, and it is not a test of whether you may drive.

Step-by-Step Usage Instructions

1STEP 1

Enter sex and body weight — together they set the body-water ratio the Widmark formula uses.

2STEP 2

Pick the drink type and how many. Each chip shows its volume in millilitres and its strength.

3STEP 3

Enter the hours since your first drink; elimination is subtracted from there.

4STEP 4

Choose a legal limit to compare against and the tool shows how long until you fall below it.

Real-World Scenarios & Practical Cases

3 Practical CasesScenario #1

Three beers over two hours

For a 70 kg man, three 355 ml beers at 5% are about 42 g of pure alcohol and peak near 0.088%. Two hours later 0.03 has been eliminated, leaving roughly 0.058%.

In a country with a 0.05% limit that is still over. Another hour is needed before it falls below.Scenario #2

What body weight changes

On the same drinks, a 50 kg person reads nearly 40% higher than a 70 kg one, because weight is the denominator in the formula.

"I was fine, so you will be" fails for a reason that is written directly into the equation.Scenario #3

Still over it the next morning

A peak of 0.12% overnight takes eight hours to clear at 0.015 an hour. Drinking late can leave you above the limit on the morning commute.

Sleep does not speed elimination up. The rate is the same while you are asleep.The Widmark formula

Pure alcohol (g) = volume (ml) × ABV (%) ÷ 100 × 0.789
BAC (%) = grams of alcohol ÷ (body weight in grams × r) × 100
Current BAC = peak − 0.015 × hours elapsed
r is the body-water ratio: 0.68 for men, 0.55 for women. 0.789 g/mL is the density of ethanol.

Pro Tips & Key Considerations

Do not use this to decide about driving. Estimates scatter widely, and reading below a limit is not the same as being safe.Drinking on an empty stomach speeds absorption, so the peak comes higher and sooner than the formula can show.Home-poured measures are usually larger than a standard drink — check the real volume and strength and adjust the count.

Frequently Asked Questions (FAQ)

Sources & References

NIAAA — What Is a Standard Drink?NIAAA — Alcohol’s Effects on the Body UK NHS — Calculating Alcohol Units