In all the ONS said some 2,529 products it monitored in the United Kingdom shrank in size between January 2012 and June 2017.
The ONS said the phenomenon of shrinkflation had not had an impact on the overall inflation figures.
They have added 1.22 percentage points to the inflation rate of sugar, jam, syrups, chocolate and confectionary since 2012. The theory goes: if a chocolate bar gets smaller but the price stays the same, that is a form of inflation because you are paying more per bite.
Chocolate bar Toblerone cut the size of standard bar by 12% from 170g to 150g last November, leaving large gaps between the peaks and angering chocolate fans. "Shrinking the size of the products being sold, whether toilet paper, chocolate or cleaning products, is a way of pushing through a price increase".
The consumer website said Tropicana Creations Pure Premium Orange and Raspberry juice has also decreased from 1 litre to 850ml, but the price in Asda remained at £2.48.
Dozens of chocolate bars and candies have already got smaller.
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It also brushed aside the idea of Brexit being a key factor behind the shrinking size of chocolate bars. Producer Mars has said it was a way of helping consumers afford the product.
The ONS also found that 614 products had got larger since 2012 but it was still markedly less than the number that had shrunk. But it pointed out that the European import price of sugar had been slowly falling since the middle of 2014 and in March 2017 it reached its lowest level since records began in 1991. They say this prevents them from having to put the cost up.
USA maker Mondelez said the move was a bid to cut costs as raw materials such as sugar and cocoa beans - a key ingredient in chocolate - have risen in price on world markets.
"Our analysis doesn't show a noticeable change following the referendum that would point to a Brexit effect", the ONS said.
A spokesman for the Food and Drink Federation, which represents United Kingdom food and drink manufacturers, said companies are facing "sharp increases" in the cost of ingredients and packaging, while the falling strength of the pound since the Brexit vote has added to "massive cost pressures".
And while the price of cocoa, another major ingredient, reached a five-year high in December 2015, it has fallen sharply over the last year.