For wine it is one 100ml glass of 12 per cent, and for spirits, a 30ml nip at 40 per cent alcohol content.
The legal alcohol limit is now 400mcg of alcohol per litre of breath for an adult driver or 80mg of alcohol per 100 millilitres of blood.
For drivers under 20 the limit is zero.
On December 1, the legal limit for adults will drop to 250mcg per litre of breath or 50mg per 100 millilitres of blood. It will remain at zero for drivers under 20.
Drivers stopped with a reading between 251mcg and 400mcg will be issued with a $200 infringement and 50 demerit points against their licence.
Drivers who accumulate 100 or more demerit points within two years are automatically suspended from driving for three months.
Like now those above 400mcg will be charged and appear in court.
The aim of the new law is to significantly reduce road trauma and is welcomed by police and road safety campaigners.
Assistant Commissioner of Road Policing Dave Cliff said staff had been handing out information and talking to drivers about the changes.
"Police welcome the lowered limit, which represents a significant opportunity to further reduce the number of people killed and maimed on our roads and lessens the lifelong impact that this has on families and in our communities," he said.
"One of the great things is that anecdotally, many drivers already appear to be taking the new limits on board and moderating their behaviour, which is fantastic to see."
Police will not be lessening their focus on those who break the law.
"While we are taking an educational approach to those drivers who fall within the soon-to-be lowered limit, those thinking that there will be any softening in our approach to drink-driving overall should think again. I can assure the public that anyone caught drink driving and breaking the law can expect to face the full consequences."
Mr Cliff said drinking driving was a factor in about 30 per cent of all fatal road crashes.
"For every 100 alcohol or drug-impaired drivers or riders who died in road crashes, 47 of their passengers and 16 sober road users die with them."
In the past decade, fatal crashes caused by drink driving have claimed around 1100 people and caused serious injuries to another 5300.
"For everyone of those people killed or seriously hurt, there are still thousands more families, friends and whanau who have been left behind grieving or struggling to support loved ones who in many cases have been left to cope with lifelong injuries."
The New Zealand Transport Agency is running a nationwide information campaign including television, radio and bus shelter advertising in the coming weeks along with posters and coasters in hotels and licensed premises.
National Road Safety Committee chairman and Transport secretary Martin Matthews said 60 per cent of Kiwis surveyed favoured the lower alcohol limit.
