Coke is reducing its can size by nearly 10 per cent, with one Wellington fizzy drink lover saying he's now short almost two cans of coke in a 24-pack.

The company has shrunk its standard can size from 355ml to 330ml.

Coke's smaller sizing was reported overseas in early 2016, however one Auckland dairy owner said he only started receiving the new size can three weeks ago.

The man, who asked not to be named, was currently selling a mix of the old and new size cans for the same price while he phased out the old ones.

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New World Victoria Park had 330ml 18-packs for sale for $20.99 on Thursday, and was selling the 355ml 18-packs for a discounted $17.99 online.

Countdown was also selling the 355ml multi-packs at a discount online, $26.00 for 30.

A Countdown spokesman said they did not influence can size and the supermarket was "currently in discussions to ensure we have the best prices we can for customers".

Foodstuffs, which owns New World and Pak N Save, has been approached for comment.

In New Zealand Coke is managed by Coca-Cola Amatil (CCA).

After being approached by the Herald, CCA communications manager Neil Waka said he would not be providing comment because he didn't have to.

When pressed, he said Coke "didn't need" media for stories because "we can do what we want" on social media.

Steve, a retiree who asked the Herald not to use his last name because he is "too well known" where he lives, said he bought a slab of coke cans every few weeks.

After bringing home a pack from the supermarket about a fortnight ago, he noticed something was amiss.

"I've got a can rack in the fridge, I put the new can in without even looking at it, and lo and behold, they fell straight through the rack."

If Steve were to buy his usual 24 pack, it meant he was short 600ml, nearly two whole cans' worth of Coke.

"I think it's a little bit devious, to be quite honest. All of a sudden, they've dropped the size."

Steve said he could understand that companies needed to raise the price of goods from time to time, but thought the size reduction amounted to "price increase by stealth".

Consumer New Zealand researcher Belinda Castles said the practice of reducing packaging was "a bit sneaky", but something producers did periodically.

Ultimately it came down to "buyer beware" and making sure you checked the unit price of products, she said.

"Companies don't want to raise the price of their products, so to get a better profit they reduce the size.

"They're entitled to do it, it's probably one way to keep the prices the same. It's a bit sneaky but unfortunately it happens across all product segments."

In 2015, Cadbury cut the size of its chocolate blocks from 220g to 200g, saying it would rather do that than raise the price.