Worked example - class B push-pull into a speaker. Supplies +-12 V, load RL = 8 ohm. Step 1: maximum unclipped peak output ~ Vcc = 12 V (ignoring saturation). Step 2: maximum load power Pmax = Vcc^2/(2 RL) = 144/16 = 9 W. Step 3: maximum theoretical efficiency = pi/4 = 78.5%, so the supply delivers Pdc = 9/0.785 = 11.5 W and the transistors dissipate ~2.5 W as heat at full power. Worst-case dissipation actually occurs around 40% of full power - which is why heatsinks are sized for mid-power, not just maximum.