Peak-Envelope Power (PEP) for SSB transmission is:

Peak-Envelope Power (PEP) is the standard method for measuring the output power of a Single Sideband (SSB) transmitter. Because an SSB signal constantly changes amplitude with voice peaks, we measure the power at the highest crest of the modulation envelope. To calculate this, we use the standard power formula P = E^2 / R, but the voltage used must be the RMS voltage at the envelope peak. To find the RMS voltage from the Peak-Envelope Voltage (PEV), we multiply the PEV by 0.707. Therefore, squaring that RMS voltage and dividing by the load resistance gives us the PEP. Calculating peak voltage times peak current would yield absolute 'peak power', which is mathematically twice the PEP and not a standard regulatory measurement in amateur radio.