Last updated: August 20, 2026
The BAC legal limit is a number written in statute — milligrams of ethanol per 100 millilitres of blood, or a US-style percentage — not a feeling of “I’m fine to drive.” This 2026 guide compares the lines that governments actually publish for ordinary licences, commercial work, and a few high-scrutiny categories, then shows why a browser calculator is an estimate rather than a roadside defense.
Figures below were checked against NHTSA, US Code, GOV.UK, Canada’s Criminal Code, and Austroads. Laws move; if you are reading this after a legislative change, trust the official page, not a cached blog. For a drinks-to-estimate sketch, use the BAC & Legal Limit Calculator.
What BAC measures and how estimates are built
Blood alcohol concentration is the amount of ethanol in a defined volume of blood. Police and hospitals measure it with evidential breath devices or blood draws. Web tools instead estimate a peak from drink count, body weight, biological sex (as a distribution-volume stand-in), and elapsed time — a Widmark-style teaching model.
NIAAA defines one US standard drink as about 14 grams (0.6 fl oz) of pure ethanol, the amount in 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits. Craft pours often exceed that. NIAAA also states that most ethanol is broken down in the liver at a roughly steady personal rate: caffeine and cold showers do not speed the enzyme clock.
CDC and NHTSA materials treat impairment as a continuum. A legal per se line is a charging shortcut, not a biological off-switch.
Common limits by country and licence type
| Place / role | Published line (verify on the official page) | Source type |
|---|---|---|
| Most US drivers 21+ | 0.08% BAC per se in the large majority of states | NHTSA impaired-driving overview |
| Utah (all drivers in that state’s per se rule) | 0.05% BAC | State per se law (in force since 2018) |
| US commercial motor vehicle (federal) | 0.04% while operating a CMV; additional out-of-service rules at any measurable alcohol | 49 U.S.C. § 31306; FMCSA alcohol rules |
| England, Wales, Northern Ireland | 80 mg / 100 mL blood (35 µg / 100 mL breath) | GOV.UK drink-drive limit |
| Scotland | 50 mg / 100 mL blood (22 µg / 100 mL breath) | GOV.UK; SSI 2014/328 |
| Canada (criminal per se) | 80 mg / 100 mL within two hours of operating a conveyance | Criminal Code s. 320.14 |
| Australia (typical full car licence) | Below 0.05 BAC in the Austroads state table; zero for many learners, P-platers, and heavy/public vehicles | Austroads Assessing Fitness to Drive, Appendix 4 |
Under-21 US drivers often face 0.00–0.02% “zero tolerance” administrative rules that are separate from the adult 0.08% criminal per se line. Those are state-specific — look up the DMV that issued the licence rather than assuming one federal youth number.
Provincial Canadian roadside programs and Australian interlock or “Z condition” licences can sit below the headline criminal or 0.05 figures. The table is a map, not your summons.
Why a BAC calculator is not proof
Absorption is still underway after the last sip. Distribution volume is not your gym weight to the gram. NIAAA notes large between-person differences in metabolic enzymes (including some East Asian ALDH variants). Evidential tests sample your body; a webpage samples a formula. Use the tool to see how drink size and time move an estimate relative to 0.08%, 0.05%, or 0.04% — then treat any plan to drive as a hard no if alcohol is in play.
Worked example: four US standard drinks vs 0.08% and 0.04%
A 170 lb (77 kg) male drinks four NIAAA-standard drinks over two hours and then waits one more hour (three hours from first sip, one hour after stopping). A simple teaching Widmark sketch uses r ≈ 0.68 for men, peak BAC ≈ [alcohol grams / (body weight grams × r)] − (β × hours), with β often taught near 0.015%/hour after absorption. Four drinks × 14 g = 56 g ethanol.
56 / (77,000 × 0.68) ≈ 0.107 (as a proportion, i.e. about 0.107%). Subtracting roughly 0.015 × 3 hours ≈ 0.045 leaves an estimate near 0.06% — under a 0.08% adult per se line in that cartoon, and still above a 0.04% CMV line. Change sex-distribution r, shorten the wait, or count a 9% IPA as 1.8 standard drinks and the same “four beers” story crosses 0.08%. That sensitivity is the lesson. Run the same story in the BAC calculator, then open the License Suspension Risk Calculator if the real-world risk is a charge plus points, not just a percentage.
Frequently Asked Questions
What is the BAC legal limit for most US drivers?
NHTSA describes 0.08% blood alcohol concentration as the illegal per se limit in most of the United States for drivers 21 and over. Utah uses 0.05%. Confirm the state statute that applies to the stop.
What is the commercial driver BAC limit in the US?
Federal commercial motor vehicle rules treat 0.04% as driving under the influence while operating a CMV (49 U.S.C. § 31306). FMCSA also places a driver out of service for 24 hours at any measurable alcohol. CDL holders should read both the per se line and the out-of-service rule.
What is the legal drinking limit in the UK?
GOV.UK lists 80 milligrams of alcohol per 100 millilitres of blood in England, Wales, and Northern Ireland, and 50 milligrams per 100 millilitres in Scotland, with matching breath and urine figures on the same page.
What is Canada’s Criminal Code alcohol limit?
Section 320.14 makes it an offence to have 80 mg of alcohol in 100 mL of blood within two hours of operating a conveyance, alongside a separate offence of impairment to any degree. Provincial administrative limits can be stricter than the criminal line.
What BAC limit do Australian full-licence car drivers usually face?
Austroads’ fitness-to-drive appendix lists below 0.05 BAC for typical full-licence car drivers in the states and territories it tabulates, with zero BAC for many learner, provisional, and heavy-vehicle categories. Check the state that issued the licence.
Is a BAC calculator proof I am legal to drive?
No. Widmark-style estimates use population averages. NIAAA notes metabolism rate is steady for a given person but varies widely between people. Food, drink strength, and timing all move the real curve. If you have been drinking, do not drive.
How many standard drinks equal 0.08%?
There is no universal drink count. NIAAA defines a US standard drink as 14 grams of ethanol. Body mass, sex-related distribution, and hours of drinking change peak BAC. Use the calculator as a sketch, then ignore it as permission to get behind the wheel.
Does coffee lower BAC?
NIAAA states the body metabolizes alcohol at a steady rate regardless of caffeine or other “sober up” tricks. Time is the only reliable reducer in that description.
Can I be impaired below the legal line?
Yes. Criminal and traffic codes set per se numbers; they are not “safe to drive” certificates. Canada even criminalizes impairment to any degree separate from the 80 mg/100 mL count.
Where do license points come in after a DUI?
A DUI/DWI often triggers both a BAC charge and separate licensing action. Model suspension risk on the License Suspension Risk Calculator; do not assume the BAC number is the only consequence.
Sources
- NHTSA — Drunk driving (US per se context)
- US Code — 49 U.S.C. § 31306 (commercial 0.04%)
- FMCSA — Drug and alcohol rules overview
- GOV.UK — Drink-drive limit (England, Wales, NI, Scotland)
- Department of Justice Canada — Impaired driving laws (80 mg/100 mL)
- Criminal Code — s. 320.14
- Austroads — Drivers’ legal BAC limits (Appendix 4)
- NIAAA — What is a standard drink? and Alcohol metabolism
Use a BAC legal limit as a charging line, not a fitness certificate. Estimate drinks against a selected line with the BAC & Legal Limit Calculator. If a charge could also hit your licence, check the License Suspension Risk Calculator.