We present a method for calculating the dielectric constant and the dissipation factor for thin-film ferroelectric capacitors from scattering parameter measurements at multi-gigahertz frequencies. Physical measurement is discussed along with description of the model upon which the calculation is based. Experimental results for 0.5 micron films of PZT are reported up to 15 GHz. Direct measurement is compared with indirectly calculated values at the 100 MHz to 1.5 GHz range, showing excellent agreement.