I have been playing with diffrent hights, over the last couple of rides, with difrent bikes... It also depends on what type of riding i am doing, if there is a lot of road i can put it a bit higher, but if there is some tricky downhill the seat may be to high. i am now runing my saddle 1cm higher than i used to, it is a lot better on the climbs and it has'nt really effected me on the downhills. I ride full sus XC (marathon, XC, and enduro racing), and Hard tail mtb's, and Cyclocross. so all my bike have had the saddles raised 1cm. Hope this helps. :)

I was always told to sit on the bike, place your heel on the pedal, and at the bottom of the pedal stroke the knee should be slightly bent. If it's too high your hips and bum will rock and you will end up hurting yourself. Too low is inefficient. I now find with SPD shoes and clips the saddle has had to be lowered slightly, but my feet are always in the right place. Off road its more reassuring if you know you can reach the ground easily. So I agree with the comments from "nezbo66" regarding bike styles and off road on road.

Ambrosini in his book 'Prendi la biclicletta e vai' gives a basic guide as follows: measure the inside leg barefoot in cms, divide by 8, multiply by 7 and subtract one. This gives a basis from which to start so adjust the saddle up, down forward or back until you feel right! The reason for this is that the dimensions of the upper and lower parts iof the leg will differ from one person to another, in fact he suggests optimal ratios for sprinters and stayers! Add to that pedal heights, shoe thickness, plates, cleats and you see that a simple calculation is not possible. ButtsBrow quotes the old British starting point which can mean either instep or heel on the pedal and work from there. This gives roughly the same starting point as Ambrosini. Sitting too high loses of power, too low may give rise to knee trouble, but only if you sit far too low.