MOSFET Power Dissipation Calculator (Conduction and Switching Loss)

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Updated October 28, 2026

A MOSFET used as a switch loses power in two ways: conduction loss from its on-resistance and switching loss during each turn-on and turn-off. Together they decide whether it needs a heat sink. This MOSFET power dissipation calculator estimates both — see what a MOSFET is and MOSFET gate driver ICs.

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Type in any field to change it. Press × on a value to calculate that field instead.

How to use the MOSFET power dissipation calculator

Enter the RMS drain current, the Rds(on) at operating temperature, the off-state voltage, the switching frequency, the total rise + fall time, the thermal resistance to ambient (or to the heat sink path) and the ambient temperature. You get conduction loss, switching loss, total loss and the estimated junction temperature.

MOSFET loss formulas

Pcond = IRMS² × RDS(on)  ·  Psw ≈ ½ × V × I × (tr + tf) × f

Tj = Ta + Ptotal × RθJA

Example

10 A, 20 mΩ, 24 V, 50 kHz, 100 ns total transition time:

  • Conduction loss = 100 × 0.02 = 2.0 W
  • Switching loss = 0.5 × 24 × 10 × 100 ns × 50 kHz = 0.6 W
  • Total = 2.6 W; with 40 °C/W and 40 °C ambient, Tj ≈ 144 °C → add a heat sink

Reducing losses

  • Choose lower Rds(on) — but larger MOSFETs have more gate charge and slower switching.
  • Use a proper gate driver to switch in tens of nanoseconds.
  • Lower the switching frequency where ripple allows.
  • Improve cooling: copper area on the PCB, a heat sink or airflow. See the heat sink calculator.

Not included

Gate-drive loss (Qg × Vgs × f), body-diode conduction and reverse-recovery losses add more in synchronous converters.

Frequently asked questions

How do I calculate MOSFET conduction loss?

P = I_RMS² × Rds(on). 10 A through 20 mΩ gives 2 W. Use Rds(on) at the expected junction temperature, not the 25 °C value.

How do I estimate switching loss?

P_sw ≈ ½ × V × I × (t_rise + t_fall) × f. Fast gate drive and lower frequency reduce it.

What junction temperature is safe?

Most MOSFETs are rated to 150 or 175 °C; design for 100–125 °C maximum for reliability.

Do I need a heat sink?

If the estimated junction temperature without a heat sink exceeds your target, yes — use the heat sink calculator to size it.

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