It is stated that there are twelve ships like the Enterprise in the fleet; few other ships are seen. The Starfleet of Earth may easily operate only these dozen vessels and assorted starbases from what is seen in TOS, as a lower limit.

As an upper limit, the NCC catalogue number may be taken as a sequential numbering of hulls; the Enterprise, not a new ship at the beginning of the show, may then be taken as the 1701st starship built. Presuming construction of NCC ships to begin roughly 100 years before TOS and roughly linear, a constant rate of 20 hulls per year would be plausible.