Which? said the shortage could be caused by manufacturers putting more effort into making bigger TVs and home cinema set ups, as smaller screens are not capable of achieving the highest resolutions.
While smaller screens might capture more detail, they are more likely to struggle displaying motion and could have a “shrill and unpleasant” sound, the group said.
However, the shift may have been driven by customer demand. The most popular size of TV with visitors to the Which? TV reviews site is now 49 inches.
Bruce Berkoff, chairman of the LCD TV Association, said the industry has driven higher quality and value for consumers at ever lower prices.
"Consumers have wanted thin and light, sleek and beautiful flat TVs at ever larger sizes, greater brightness, with just amazing picture quality," he added.
Standard size TVs are no longer worth the money, Which? has said as only screens above 32 inches provide a good viewing experience.
The consumer group said that shoppers looking for a smaller TV to fit their living room are being left disappointed by sets that “consistently fail to deliver the sound and picture” of their bigger, and more costly, rivals.
Which? tests hundreds of TVs each year and said it has not given a positive review to a set with a 32 inch screen or smaller since 2014, despite having labelled 200 larger versions as “best buys”.
There are also less options for those who prefer a smaller screen compared to several years ago as Which? said manufacturers now sometimes include only one in their range.
Natalie Hitchins, Which? head of home products, said: “When it comes to TVs, size definitely matters - bigger models score consistently better in Which? testing but while smaller TVs are in much less demand than they used to be, there still appears to be a gap in the market for small sets that really pack a punch.
“Our advice to shoppers is to choose a larger TV that they can comfortably view, where possible. For small or occasional spaces, streaming content on a laptop or tablet may just offer a better experience than a small TV.”