The RIBA report warned that space constraints mean families do not have the space they need to live "comfortably and cohesively", accommodate a growing family or ageing relatives, or to store everyday items, such as a vacuum cleaner.
Its report said the average new-build three-bedroom home outside of London is 4 square metres smaller than the new nationally described space standard introduced in October.
Houses in Yorkshire were the smallest in England, it found.
The average three-bed home in Yorkshire was 25 square metres smaller than in London - the "equivalent of a double bedroom and a family living room", RIBA said.
RIBA said the new space standard does not apply to all new homes, pointing to exemptions on office-to-residential conversions.
It is urging the government to introduce a national space standard that applies to all homes, in every location.
RIBA president Jane Duncan said: "Tiny rabbit-hutch new-builds should be a thing of the past. But sadly our research shows that for many people, a new home means living somewhere that’s been built well below the minimum space standard needed for a comfortable home.
"We urgently need new homes, but building small homes or cutting corners when converting office buildings to flats is short-sighted and fails the people these new homes are meant to serve. The government must take action to ensure a fairer minimum space standard is applied to all new homes across the country."