Maximum Power Transfer Calculator

Maximum Power Transfer Formula

Worked Example

A source with V_Th = 12 V and R_Th = 4 Ω:

1. Maximum power when R_L = R_Th = 4 Ω
2. P_max = V_Th² ÷ (4 R_Th) = 12² ÷ (4 × 4)
3. P_max = 9 W

Efficiency at maximum power: 50 % · Power into R_L = 8 Ω: 8 W · Efficiency at R_L = 8 Ω: 66.66666667 % · Load current at maximum power: 1.5 A

GATE tip

If the load is fixed and R_Th is variable, the maximum power transfer theorem does not apply: power is greatest when R_Th = 0. Read the question for which resistance is adjustable.

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Frequently asked questions

Sources

• The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.