Blood Alcohol Range Calculator
Estimates a blood alcohol concentration (BAC) range from drinks, weight, sex and time using the Widmark method.
Enter your details
A “standard drink” isn’t the same everywhere — Australia/NZ use 10 g of pure alcohol, the US 14 g, the UK 8 g.
Used only for a rough body-water estimate — it doesn’t account for your individual body composition, hormones or metabolism.
If you’ve stopped drinking, enter the current time — the sober hours since your last drink are counted as extra elimination. Leave blank to estimate right at your end time.
Count standard drinks for the country/system selected above.
Estimated BAC range
Enter your details and press Estimate range to see an approximate BAC range. This is an educational estimate only.
Before you rely on this: Safety-critical: treat this as a preliminary check only. Always verify against the governing standards and have a competent person review the result before use.
How to use this calculator
- Choose your country / standard drink system (or enter custom grams of pure alcohol).
- Set the body-water estimate, your height and weight, and the drinking start and end times.
- Enter the number of standard drinks and how they were spread out, then press Estimate range.
How it works
This tool estimates a possible blood alcohol concentration (BAC) range from your country's standard drink size, weight, sex-based body-water estimate, height and drinking time — an educational estimate only, never a guide to whether you can drive.
It uses a simplified Widmark-style model with low, middle and high assumptions for body-water distribution and how fast alcohol is eliminated, so it shows a range rather than a single false-precision number. Standard drink sizes differ by country (Australia/NZ 10 g, US 14 g, UK 8 g), which is why the country selection matters.
Worked example
5 Australian standard drinks, 80 kg, over 3 hours. 5 × 10 g = 50 g of pure alcohol. The calculator returns an approximate BAC range with a likely middle estimate — not a single exact figure.
Tips
- If you have consumed alcohol, the safest choice is not to drive — plan ahead and use a safe ride.
- Alcohol can remain in your system for hours after drinking; this tool cannot confirm when you are safe or legally allowed to drive.
Frequently asked questions
Is this BAC calculator accurate?
No — it provides an approximate range only and cannot replace a real breath or blood test. Many factors it can't see (food, medication, fatigue, health, body composition, metabolism) change your actual reading.
Can I use this to decide whether I can drive?
No. Do not use this result to decide whether to drive. If you have consumed alcohol, the safest choice is not to drive. Only an approved breath, blood or law-enforcement test gives a legally reliable reading.
Are standard drinks the same in every country?
No. Standard drink definitions vary — for example Australia uses 10 g of pure alcohol while the United States uses 14 g. Choose the matching country or enter custom grams.
Why does the calculator show a range?
BAC varies with body size, metabolism, sex-based body-water estimates, food, medication, drinking speed and more, so a single number would imply false precision. A range better reflects that uncertainty.
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Cite this tool
Zerdly. (2026). Blood Alcohol Range Calculator. Retrieved from https://www.zerdly.com/tools/blood-alcohol-range-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.