Can someone please explain, link to what i need to read to understand the figures and how that affects the bike fitting.

Surely just buying a bike thats a large for a 6 footer would be adequate…i ask after seeing this post from Tomaso as these are the bikes im considering

I have geeky spreadsheet listing geometry and all important reach. My Pitch(480mm but reduced with Lyrik and offset bushes to 458mm is long and has plenty of reach and the YT is a fair bit shorter at 443mm and does not have an XL option.
The XL/L reach figures for bikes I’m pondering are:
Mega 275 – 438-465mm
Specialized Enduro 29er – 445-465mm,
Kona Process 153 – 46p-485mm,
Mondraker Foxy – 501-508mm,
Dune – 480-496mm,
Whyte G150 – 477mm
SJ Evo29er – 435-456mm,

Longer front centres seem to be where its at with Mondraker Iona and the new Canyon Strive Race all pushing things that way. I am therefore inclined towards something nearer the Pitch in reach.

These problems didn’t exist when geometry was fixed back in the rigid early 90s…

http://singletrackworld.com/forum/topic/go-shopping-for-me-2k-lakeland-monster#post-6097853

Surely just buying a bike thats a large for a 6 footer would be adequate

1st point large is a word not a size, different companies make different sized large bikes so it’s got no real meaning.
2nd 2 6ft people can have very different arm and leg lengths hence stand over and reach are important.
3rd Height/leg length was great for road bikes and hard tails but with low standover things are very different. I can ride most XL frames for standover but reach I’d have no chance.
Thats the basics for why height based sizing is bad.

First thing to do get on the bike and try it.
After that if you can’t make sure you can return it.
The find a geo chart for the bikes your interested in

then measure against what you have that fits.