The jail was designed to hold 318 inmates but the Howard League for Penal Reform says at the end of January, there were 530.
The charity also says the overcrowding leads to more violence and self-harm among prisoners, and hampers their rehabilitation.
Devon voters go to the polls
A third of Plymouth City Council seats are up for grabs
Clyst valley park could double in size
Residents will have their say
Multiple arrests made in Exmouth
Patrols stepped up to tackle big issues
Devoncast - Exeter Pride, Torbay tourism and Tavistock trains
Devoncast features the latest news and views from around Devon
Sid Valley Radio joins East Devon broadcast bid
New digital stations planned for East Devon
