Welcome Gary, you are in the right place
I think it's a bit more than 30 metres of the 25 square, about 33 from memory. I bought one of Handyandy's superb flat pack kits so didn't have to work it out in the end.
I think there are quite a few other builders that are also in to bikes so you are in good company.
This is a great resource, my project would be miles further back if not for the help on here, there are some very clever people pop in.
All the best,
Enoch