How are the dimensions of the empennage determined for jetliners?
The tail volume coefficients for the horizontal stabilizer ($C_H$) and vertical tail ($C_V$) for jet transports are 1.00 and 0.08 respectively.



For the horizontal stabilizer, for example, with the $C_H$ given, and the lever arm, [main] wing reference area ($S_W$), and MAC known, the area can be calculated.

The shape, sweep angles, aspect ratio, etc., of each surface have their own rules.* Knowing the shape and area, the span or height is calculated.

Example 1: When the lever arm was reduced when the A319 was shortened to become the A318, they had to compensate by increasing the vertical stabilizer area, which meant a higher tail.

Example 2: Boeing designed the 757 and 767 simultaneously, so in order to reduce the fabrication and tooling costs, both shared the same tail, with the 757 tail shortened at the root (Flight, 1979).

(Own work)



* Reference and further reading on the aforementioned rules: Empennage General Design (.pdf), Hamburg University of Applied Sciences.