Ok, so the prevailing view is that anything 6'10" and under is a short board, with 7'0" to 8'0" being a mid-size, and longboard being anything bigger than 8'0" - with the purists saying 9'1" and above is a true LB.
Just wondered how 9'1" became the standard 'starting' LB size? Is it because the blanks start at 9'2" ??
It might have been from the 60's??? I understand that boards have always had to measure up to a 9'0 measuring stick, and a 9'1 usually covers 9'0... Especially if you add a tail block or a nose block!
History mainly, Sam was 9'2 and then pretty much boards went down from there so when guys started riding LBs again the went to where they stopped 9 footish.
And most comps and even the AsP even says 9'0 and greater then about 22" for there comps so that backed it up I guess.
But under 9 ft is not a LB IMO. And standard LB is greater than 9'0 wider than 22 and a nose bigger than 16, rounded not pointy.
Edit... I'll add
I never understood the 9'1 either... Still don't 
9'0 to 9'6 was a very popular length back in the 60's too... Surfing had been going for long enough for people to realise that 10'0 was just a little bit too big for fit strong & young 22 year old males...
But 10'0 can be about right at the age of 50 to 60! Or for more solid muscly guys... 
Bob McTavish was always a little bit smaller than average, and he shaped a few shorter boards for himself in those early days... and then George Greenough showed them what could be done on a 4'6 kneeboard with a refined marlin fin... and the rest is history really!!
9'1 matches the age of the average long boarder- 91 years old.
that's why mac's boards are getting longer
couldn't be anything else
I don't think you blank boards by length or width alone...
But generally 7-9 is Midlength... Under or over is short or long...
But an 8'2 McTavish Involvement is a Longboard in my book...
But an 8'0 Bobsled is a Midlegth...
An 8'1 
Ball is a midlength meeting a Longboard... *
But one this is for certain, Chrispy's Ball had heavier concaves than average!
* this is an eightball... http://www.mctavish.com.au/surfboard/eightball
McTavish call it a midlength.
Ball is a midlength meeting a Longboard... *Ball had heavier concaves than average! 
Because only real men can handle a 9.1.
9 foot and over for any comp,they made 9.1's way back because a guy got pulled up for surfing a comp on a 8.11 the shaper fked up,fact.
Funny Mac! But they are Bobby Diamond Boardies... You like them too!
Good one SP!
More fish!
funny thing is I'm wearing the same as you in the pic but red and black boardies and white mct tee,scary
Seeing I have repented and sold all of my surf sups am I allowed in the longboard room?
When you want glide there is only one board and it aint a Mc T.
Foiled rails to fool the water into thinking the boards are thin, subtle concave in the nose for nose rides, three fin options to allow broad range tuning for conditions and advanced (forward) vee so you don't have to be on the tail to turn. This surfboard is fast, fast, fast.
12'0" x 26.25" x 4.25"
2+1
Squash Tail
Tuflite
Phill
and it aint a Mc T.
Welcome OG - what about a nice thick and heavy PU board like Big Spaz rides - those things have more glide than a glider itself! Although they are not much fun to walk down to the beach with
and it aint a Mc T. 
four and a quarter
