Finding the right length of chain lock for my road bike I am trying to buy a chain lock as I would be leaving my cycle in quite a busy area. I am not sure what length of chain lock I will need if I wanted to secure my bike using a chain that runs through both the wheels and the frame. 

The 90cm Kryptonite looks two small to run through two wheels, 
I am not sure if I need two 1m chain locks or if I could do with one 1.5m chain lock

I looked at the pragmasis protector 16mm chain lock with padlock. Anyone have any advice specifically on what length of chain lock i will need or if it is better to get two short chain locks both for the front and the back wheels
I faced the same dilemma a while back.
Getting a big chain implies carrying way too much weight around. Even a small, good bike chain is pretty heavy and can easily be 1/3 the weight of your bike.

The best way to protect your bike and be able to carry the locks around is to have a chain or a U-Lock, and with these you can easily secure your frame and a wheel, and then use a small cable like this to secure the other wheel. One wheel is less protected, but a substantial part is under a good lock and the weight is not too bad.

From these I actually prefer a small chain to a u-lock because it is easier to lock the bike to a tree for example, but if your city is bike friendly a u-lock offers very good protection and is much more manageable.

When buying locks keep in mind price usually means security. I recommend you check the independent tester of locks Sold Secure. They have a catalog with different locks they have rated.