Astralsource -
Please refer the link for the details on the pool size.
http://www.cicnews.com/2016/11/express-entry-human-capital-skills-experience-more-prominent-under-new-system-118705.html
October 3 snapshot of the pool
As of October 3, there had been 20 rounds of invitations (draws) so far in 2016. The snapshot of the pool on that date revealed that:
There were 60,689 candidates active in the pool.
A total of 20,588 ITAs had been issued to 19,088 individual candidates over the first 20 draws of 2016. (Note: some candidates may obtain more than one ITA. For example, if they receive an ITA but don’t feel ready to apply, they may re-enter the pool and be issued another ITA at a later date.)
From January to September, 2016, a total of 25,406 Express Entry candidates or their accompanying family members landed in Canada as permanent residents.
From this glimpse into the pool, it is apparent that around one in every four candidates who was actively engaged in the Express Entry system over the first nine months of 2016 received an ITA. Indeed, there have been four further draws since October 3, and the number of ITAs issued has nearly doubled from 1,288 (September 21 draw) to 2,427 on November 16.