Drink Drive Calculator

Alcohol contributes to around 30 percent of New Zealand’s fatal road crashes. Over the last 10 years, fatal crashes caused by drink-driving have claimed the lives of around 1,100 people and caused serious injuries to another 5,300.

From 1 December 2014, the alcohol limit lowered for drivers aged 20 years and over. This has created confusion and people are unsure of how much they can drink before being over the legal driving limits.

You can use our calculator below to ESTIMATE your Blood Alcohol Level (BAC)

Before you do though, please read the notes below !!

  1. Our calculator is based on the Widmark Formula found here.
  2.  There are many factors which will determine how quickly alcohol is absorbed into your system, including body type, gender, weight and food intake. Even small amounts of alcohol affect your judgement, and the ability to drive safely begins to deteriorate after even one drink.
  3. It is important to remember that there is no ‘safe’ level of alcohol for driving, and the best advice is to keep it simple and avoid any doubt by making the choice not to drive if you are going to drink. Call a taxi, take a bus or get someone who hasn’t been drinking to drive you home. Think ahead – it’s always easier if you have a plan.
  4. Guidance from the Institute of Environmental Science and Research (ESR) indicates that most adults may be able to drink two standard drinks over two hours and be likely to remain under the new drink-driving limits for adults.
  5. A standard drink contains 10g of pure alcohol. This is approximately to equivalent to 330ml of beer, 100ml of wine or 32ml of straight spirits, containing 4, 12.5 and 40 percent alcohol respectively.
  6. In New Zealand, the label on the packaging of an alcoholic drink must state the approximate number of standard drinks it contains. If you are buying something by “the glass” or out of it’s original packaging ask the bartender how many standard drinks it contains. They should be able to tell you. If they can’t ask for the duty manager. If they can’t tell you suggest that as part of host responsibility they really SHOULD be able to.
  7. A “Standard Drink” is worked out as follows.

Size of drink in milliliters (volume) * Percent by volume of alcohol (%) * Density of ethanol at room temperature (0.789) / by number of grams in a standard drink (varies by country. In New Zealand it is 10 grams)

(standard drinks = volume * percent * 0.789 / 10)

To use the calculator:

First work out how many standard drinks you have had.

A can of beer normally contains 330 ml at 5 percent alcohol by volume with WHO ‘standard drink’ definition of 10 g:

(ie: 330 x 0.05 x 0.789 / 10 g = 1.3 (approximately 1.3 ‘standard drinks’)


Once you have determined the total number of standard drinks enter that number, your weight and the time spent drinking into the form below.

Note this is an ESTIMATE based on an accepted formula. A number of factors can alter the actual level and we take no responsibility whatsoever if you decide to drive after drinking.


Now you know your estimated BAC level you can decide if you should drive or not.

If you choose to drive after drinking the penalties are described below.

Drivers Under 20

In New Zealand there is a ZERO alcohol limit for all drivers under 20 years of age.

For all drivers aged 20 or over

0.05 – 0.08 BAC

If you drive from  0.05% – 0.08% BAC (500 mg/L to 800 mg/L) you will be instantly fined $200 and earn 50 demerit points)

Over 0.08 BAC

If you drive over 0.08% BAC (800 mg/L) you will be required to appear in court where the following penalties may be imposed

    • For 1st and 2nd offences you will receive a minimum of 6 months loss of license plus a fine of up to $4500 and/or up to 3 months imprisonment.


  • For  3rd and subsequent offences you will receive a minimum 1 year loss of license plus a fine of up to $6000 and/or up to 2 years imprisonment.