The phenomenon is known as "shrinkflation" because while the price of an individual item stays the same, the cost per gram goes up.
The ONS said that since 2012, 614 products had got bigger.
However, the overall impact of shrinkflation is relatively small: it added around 0.03 percentage points to the rate of inflation over the last five years.
But among sugar, jam, syrups, chocolate and confectionery, the difference was stark. When these products are taken in isolation the rate of inflation was 1.22 points higher when changing pack size was taken into account. This has been particularly felt since January 2014.
Cutting the size of a product can be a contentious move for brands. Mondelez caused a social media backlash last November when it announced it was changing the shape of its Toblerone chocolate bars in order to reduce the weight of the product without changing the size of the packaging.