The figures compare favourably with other European leagues - the English Premiership averaging over 11,500 during their regular season, and the French Top 14 currently standing at around 12,300.
However, the Magners League fanbase has expanded at twice the rate of their English counterparts, 20% up compared to 10% .
Director of Celtic Rugby David Jordan said: "The increase in the average gates reflects the interest shown in the Magners League over the season.
"This has been facilitated not only by our teams playing in some of the best rugby stadia in Europe, but also the loyalty of our supporters and of course the quality of rugby on display.
"The hard work put in by the backroom staff behind the scenes has been reflected in the fact that attendances for games in Scotland alone have increased by over 45%, whilst Magners League champions Munster are amongst the top-three supported teams in Europe.
"In difficult times this is a tremendous achievement and congratulations must go to all involved at the clubs, and of course our thanks to all those loyal supporters and new fans who followed their teams throughout the season.
"With the Cardiff Blues moving to their new ground and redevelopments at Ravenhill and Rodney Parade, we can look forward to reaching out to even more fans during the 2009/10 season."