Research by Which? suggests some brands of toilet rolls, biscuits and fruit juices have shrunken considerably - but many shoppers are unaware they are effectively paying more for less.
The weight of a typical pack of McVitie's dark chocolate digestives was recently decreased from 332g to 300g, a reduction of 10%, yet prices in Tesco (Xetra: 852647 - news) are 10p higher than they were before.
Meanwhile, Asda left the cost of Tropicana's orange and raspberry juice at £2.48 - even though the carton size had been slashed from a litre to 850ml.
You may have thought your household was going through Andrex toilet paper at a rate of knots, when in fact the number of sheets on each roll has dropped from 240 to 221.
Despite this, the price of four rolls has remained around the £2 mark.
In some cases, prices have been lowered when a product has become smaller - with Sainsbury (Amsterdam: SJ6.AS - news) 's and Waitrose reducing the cost of Percol fairtrade Guatemala coffee when the serving went from 227g to 200g.
But even then, shoppers have been left paying more per 100g than they originally were.
Several brands responded to the research by stressing it was up to supermarkets to decide their prices, but they did not reveal whether they had charged lower wholesale prices for the shrunken products.
Four in five consumers polled by Which? believe it is wrong for groceries to get smaller and cost the same - especially if shoppers aren't told about the changes.
The organisation's editor, Richard Headland, said: "Shrinking products can be a sneaky way of increasing prices. We want manufacturers and supermarkets to be upfront about shrinking prices so consumers aren't misled."