It isn't that simple.
In order to do it most accurately, you need to determine input signal levels, signal differentials, antenna gain, and distribution losses (which includes the coax). It there's sufficient signal margin, an amp isn't needed at all. If the signals are quite strong, an amp will cause a loss of reception. OTOH, if all signals are very weak, then a premp added to a properly selected antenna will improve the overall system performance and help prevent reception loss when signals fade due to atmospheric changes.
Tech support for Antennas Direct