Appendix D Useful tables and formulae
The deciBel (dB) represents a logarithmic ratio between two quantities. Of itself it is unitless. If the ratio is referred to a specific quantity (P2, V2 or I2 below) this is indicated by a suffix, e.g. dBμV is referred to 1μV, dBm is referred to 1mW.
Originally the dB was conceived as a power ratio, hence it is given by:
Power is proportional to voltage squared, hence the ratio of voltages or currents across a constant impedance is given by:
Conversion between voltage in ...