I'm having a new chimney built and I understand the 2-10-3 rule regarding height. But I don't know if I'm allowed to include a chimney cap as part of the measurement. Any help appreciated.

No, the cap should not be included in the minimum height requirement.

Thanks for the information! It was helpful in dealing with the county inspector and the contractor.

Great!
(those are definitely guys you don't want to irritate!)