Feltham prison is one of the least overcrowded facilities in England and Wales despite there being a national increase in prisoners over the last two years.
According to statistics from the Ministry of Justice, the maximum number of inmates that the jail can hold - and be seen as providing a good standard of accommodation, known as Certified Normal Accommodation (CNA) - is 650.
Figures from February 2015 show the actual number of convicts locked up at the Feltham Young Offenders' Institution stood at 528 - well below the prison's CNA capacity.
With the prison at just 81% capacity, this makes it the seventh least overcrowded in England and Wales.
Elsewhere in west London, Wormwood Scrubs prison, near White City, is overcrowded operating at 109% of its CNA with 1,258 prisoners crammed into a space meant for just 1,156.
Prison overcrowding has grown throughout the country over the past two years with 84,000 prisoners having to squeeze into accommodation that is only designed for 75,000 at the last count.
This equates to 112% on the CNA level and is 6% higher than it was in February 2013.
Out of the 119 prisons in England and Wales, 71 are currently operating above their normal accommodation capacity and the volume of prisoners relative to this normal capacity has increased in 75 prisons since 2013.
