Chain length on Trek 8000 bicycle?

[mommy of 1, more to come]

How long should the chain be for a TREK 8000 bicycle? Or in other words how many links should be on the chain?

I got a new chain for my bike and don't know what is correct for the chain length for my particular bike. I know that it is important to not have a chain that is too long or too short and taking it to a bike shop is pretty expensive. Please only answer if you know for the TREK 8000 specifically. Thanks.

 

[bob a]

Here is how you do it.

http://bicycletutor.com/calculate-chain-length/