Toilet roll, chocolate biscuits, orange juice and antibacterial wipes were all on the list of shrinking items reported by Which?.
The consumer group argued that making products smaller was a "sneaky way" of increasing prices.
It is further evidence of a trend towards shrinking products.
In January Unilever revealed that a number of ice creams it makes would be getting smaller.
The latest list from Which? includes:
Most brands, responding to the Which? research, said it was up to supermarkets to set the price. However, they would not disclose if they had charged the stores a lower wholesale price.
"Shrinking products can be a sneaky way of increasing prices. We want manufacturers and supermarkets to be upfront about shrinking products so consumers are not misled," said Which? editor Richard Headland.
A consumer group has revealed its latest list of shrinking supermarket items that still cost the same, or more.