Legal alcohol limit for drivers in the United States

For decades states chose their own limits, and many used 0.10. Federal highway funding rules encouraged every state to adopt 0.08, and by the mid 2000s all of them had done so. The figure reflects research showing that crash risk climbs steeply as blood alcohol rises, and that most drivers are clearly impaired by that point.

The 0.08 rule is a per se law. Per se means that the number itself is the offense. A driver who tests at or above it can be charged even if they appear steady, drove carefully and feel fine. Separately, every state also allows a charge for driving under the influence based on observed impairment, which can apply at any level.

• Per se offense at 0.08 or higher for adult drivers in most states
• Impairment based charges possible at lower levels
• Breath and blood results can both be used, under each state's procedures

Utah lowered its adult per se limit to 0.05, the strictest in the country, and the change took effect at the end of 2018. Visitors are held to the same rule as residents. Utah also applies a strict standard to drivers under 21, which our state table covers.

For a typical adult the gap between 0.05 and 0.08 can be a single drink. Our bac chart shows how quickly an average person reaches each level by weight and number of drinks.

Anyone operating a commercial motor vehicle that requires a commercial driver's license is held to 0.04, set at the federal level and enforced by every state. The rules come from the Federal Motor Carrier Safety Administration, known as FMCSA, and apply while the driver is behind the wheel of a commercial vehicle.

Federal rules also take a driver out of service for 24 hours if any measurable alcohol is detected while on duty, even below 0.04. Employers in regulated transportation run their own alcohol testing programs under 49 CFR Part 40, which our guide to dot breath alcohol testing explains. A commercial license holder can also lose that license after an offense committed in a personal car.

Because the minimum legal drinking age is 21, every state has a zero tolerance law for younger drivers. In practice the threshold is usually 0.02 or lower. Some states set it at 0.00 or 0.01, and the low figure exists mainly to leave room for measurement error and trace amounts rather than to permit any drinking.

Consequences under these laws usually start with a license suspension and can grow quickly. If you are a parent thinking about home testing, our guide on a breathalyzer for teen drivers covers the practical side.

Many states add a second, higher threshold that triggers stronger penalties. Depending on the state it is often set somewhere around 0.15 to 0.20, and the labels differ, such as aggravated, extreme or high BAC. Crossing it can mean longer license suspension, higher fines, mandatory treatment, jail time or a required ignition interlock device. Because the numbers and penalties vary a lot, check your state DMV or state statutes for the exact rule.

Every state has an implied consent law. By driving on public roads you are treated as having agreed in advance to a chemical test of breath, blood or sometimes urine when an officer has lawful grounds to request one. Refusing an evidential test usually brings its own administrative penalty, most often a license suspension, which can apply even if you are never convicted of impaired driving.

Implied consent covers evidential testing, usually done on an approved instrument at a station or with a blood draw. Rules about preliminary roadside breath tests differ by state. The details, including the length of suspensions, are set by each state, so the state DMV is the place to confirm them. Our police breathalyzer guide describes how roadside screening and evidential testing differ.

Operating a boat under the influence is illegal on US waters. Federal rules for recreational vessels use 0.08, commercial vessel operators are held to 0.04, and states enforce their own boating laws on top of that.

Pilots follow Federal Aviation Administration rules. A pilot may not act as a crew member with a blood alcohol concentration of 0.04 or more, or within 8 hours after drinking any alcohol. Many airlines apply stricter internal policies.

• National Highway Traffic Safety Administration (NHTSA), for national impaired driving data and research
• Your state Department of Motor Vehicles (DMV) or state highway safety office, for the limits and penalties that apply to you
• Federal Motor Carrier Safety Administration (FMCSA), for commercial driver rules
• 49 CFR Part 40, for workplace alcohol testing procedures in regulated transportation
• Federal Aviation Administration (FAA), for pilots
• US Coast Guard and your state boating agency, for boating

A legal limit only helps if you know roughly where you stand, and even then it cannot tell you that driving is safe. The bac calculator estimates a range from what you drank, and a personal breath tester gives a reading from your actual breath. For readings you can trust, a fuel cell breathalyzer is the sensible choice, and our best breathalyzer ranking compares models by use case. The safest plan does not depend on any number at all: arrange a ride before you start drinking.

A calculator only estimates. To measure, a fuel cell breathalyzer reads your actual breath.