The St. John's Outer Ring Road length (Northern section) is listed as 20 km.
http://www.releases.gov.nl.ca/releases/1999/wst/1115n07.htm
From Google earth, the southern portion of the ring road (Pitts Memorial/Harbour Arterial) is about 14.4 km.
From Google earth, the total of the two routes forming the St. John's ring road is about 35 km.