The answer is, you don't.

As of May 20, anyone caught drink-driving in NSW at any level, including low-range, can lose their licence immediately and face a $561 fine, with infringement notices issued to first time low-range offenders meaning they can avoid facing a court altogether.

Ebony Worland, treasurer of the Ariah Park B&S said she has been involved in the event for seven years and can always remember offering a breathalyser service for punters.

"They are there from 7am until about lunchtime," she said. "One of the reasons we started offering it was to help out the police because there are a lot of people leaving at one time," she said.

"We wanted to do our part to keep the road safe.

"People can double check because you never know what your blood alcohol content is, but you can't use them legally. It is more of a guide."

Ms Worland said the committee constantly gets the devices recalibrated and will also upgrade them when needed.

"We pay the cost," she said.

"When the reading comes up, we don't give advice.

"We say these are just a guide and it is up to the individual."

With the new law, if you blow a 0.049 reading, you're off the hook but if you blow a 0.05, then you lose your license for three months.

"I think at the next ball, we will see more people use the breathalysers we offer," Ms Worland said.

Jon Morgan, the founder of the local Traffic Offenders Intervention Program, said when it comes to knowing if you are over the limit, the key message is that everyone is different.

"You have to consider your body weight, fitness, kidney function, propensity for absorbing alcohol and when you last ate," he said.

"There are a lot of factors that come into it. Everyone is different, there is no set of rules.

"Then the question is, 'how do I judge it?' You don't."

Mr Morgan said with courtesy buses, Uber and taxis, people don't have an excuse for not having a "Plan B" after going out for a drink.

"If you drink 10 beers, that is 10 to 12 hours minimum for you to become under the limit," he said.

Mr Morgan hopes the government will ensure educational programs will coincide with the new laws to ensure people are aware of the reasoning behind it and how blood alcohol content works.

"I think they should make it mandatory to do the Traffic Offenders Intervention Program," he said.

"Bring this legislation in, but with it you have to have the education alongside it."

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