Calculate stick lengths for a given diameter using hubs
These automatically account for the space that hubs take up and give you the stick lengths to cut for a given diameter.
Third party calculators
There are lots of resources online, here are a few that might be useful.
Acidome - a very cool calculator which enables you to input specific wood sizes, calculate triangles sizes, the base and see the basic cover applied to the structure!
Domerama - lots of calculators with lots of information and detail. Can be a bit overwhelming for the uninitiated!
Desert Domes - simpler than domerama, also has a useful overview diagram accessible from a link at the bottom of the calculation table.
Geo-dome - a range of calculators including calcs for wind and snow loads.