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's NHS struggling to afford redundancies
Efforts to save a record £256 million are being hampered
Call for Torbay memorial bench price hike review
Bay's charges even outstrip Westminster's
Tamar Tag admin fee to rise by 150 percent
It's a "common misconception" that it's profit making
£60k to connect one home to fibre broadband
Connectivity issues prompts council to lobby for progress
Devon charity recieves money from Ricky Gervais
It's part of a wider £2.5 million donation
Exeter to get 'urgent' solar panels
The council will borrow money to fund them
