There's actually no direct (or even related) formula for RMS - PMPO (bullcrap PMPO).. As per definition from National Semiconductor's Audio Radio Handbook "PMPO is the maximum power an amplifier can deliver to a load with sagging the power supply". And as per FCC rule, bawal mag advertise ang amplifier with PMPO ratings, it tends to fool the consumers. Imagine, seeing an amplifer with PMPO rating of 200W/Ch and a 25W RMS/Ch... GRRRRRR kakainis