A digital signal meter will give the information several ways , dBm , SNR , signal quality and more , those meters are high dollar. An older analog meter can be used to measure general digital signal level , but with digital there is more to it then signal level. Yes it can be calculated with out meters , requires more information and thought. I will present some basic information. And the others can provide more info. The FCC reference point for digital Tv reception is 0 NM(dB) , the reference 'cut to channel antenna' is a simple 2 element dipole 30 feet high above the ground and LOS Line of Sight transmission and reception known as perfect reception conditions. . Here is more information
http://forum.tvfool.com/showthread.php?t=109