Ski Length

What determines Ski Length?
I understand the type of ski makes a difference. I'm interested in Freestyle Skii-ing but only general, not specifically one discipline.
So all-round twin-tips seem to be the thing to go for, but there are several different lengths...
Any help appreciated.

Cheers

I always thought that the rule of thumb is to go for a ski that is reaches between your chin and nose. Any longer and they will be a pain to swing around in the bumps and too short and they will not be stable enough on piste (Plus may sink in the powder).

How tall are you?

I'm 5'8" and have 175cm Dynastar TroubleMakers. I use them as all round ski's as they are just about wide enough under foot for occasional foray's into the powder, stiff enough for carving on piste and versatile enough for the park.

Demonic
There is no one rule for ski length now!
Three factors must be considered;
1.Your ability level
2.Skiing type you will do
3.Skiing terrain you will mostly be on.

Let me illustrate
On hard race course type run,,, I ski a 165 cm Atomic SL12

On powder snow up to my chest I ski my Atomic Sugar Daddys at 180 cm +

On varied terrain with crud, soft snow I ski with Rossi Z9 170 cm.

If I had one rule for beginner skiers it would be get a ski that is between nose and forehead!