Maximum Power Transfer Calculator

About this calculator

The maximum power transfer theorem states that a load draws the greatest possible power from a source when the load resistance equals the source's internal resistance (its Thevenin equivalent resistance). This calculator takes a source's voltage and internal resistance and computes both the optimal load resistance and the maximum power that can actually be delivered to it at that matched condition.

This principle guides circuit and audio engineers when matching a speaker's impedance to an amplifier's output impedance, sizing antenna-to-transmitter interfaces in RF design, and designing power-transfer stages generally — though it's worth noting the theorem maximizes delivered power, not efficiency: at the matched point exactly half the source's power is dissipated inside the source itself, which is why power-distribution systems deliberately use a low source impedance relative to the load instead.