MOSFET Gate Resistor Calculator

Created: 19/03/2026Updated: 13/06/2026By: Mert
MOSFET Gate Resistor Calculator
RG = Vdrive / Ipeak
ton ≈ 2.2 × RG × Ciss
Ipeak = Vdrive / RG
MOSFET Gate Resistor Calculator
Vdr Drive Voltage
Gate driver output voltage
Ciss Input Capacitance
pF (from MOSFET datasheet)
RG Gate Resistor (target)
Enter to find turn-on time, or leave blank for recommendations
Enter values
MOSFET Gate Resistor Calculator Results
RG
—
Ω
Turn-On Time
—
s
Peak Igate
—
A
Gate Charge Qg
—
C
Drive Power
—
W
Frequency
—
 
MOSFET Gate Resistor Calculator Input Output

Figure 1: MOSFET Gate Resistor Calculator — enter values to calculate the result with step-by-step workings.

Table of Contents
Fundamentals
  1. Why MOSFETs Need a Gate Resistor
  2. The Formulas
Worked Examples
  1. Small-Signal MOSFET (1 nF Ciss)
  2. Power MOSFET (10 nF Ciss)
Deep Dive
  1. Speed vs EMI Trade-Off
  2. Split Gate Resistors
Reference
  1. Frequently Asked Questions
  2. Related Calculators

Why MOSFETs Need a Gate Resistor

A MOSFET gate is a capacitor. When the driver output switches, it dumps current into that capacitance as fast as the driver can supply it. Without a gate resistor, the peak current can reach amps, the voltage overshoots and rings, and the fast dV/dt radiates EMI across the PCB. The gate resistor limits the peak current and controls the turn-on speed — trading a small increase in switching loss for dramatically cleaner waveforms.

The calculator above takes drive voltage, Ciss (input capacitance from the MOSFET datasheet), and a target gate resistor value, then returns the turn-on time, peak gate current, gate charge, and drive power. The MOSFET Calculator analyses the drain-side operating point once the gate is fully driven.

The Formulas

Turn-on time: ton ≈ 2.2 × RG × Ciss
Peak gate current: Ipeak = Vdrive / RG
Gate charge: Qg = Ciss × Vdrive
Drive power: P = Qg × Vdrive × fsw

The 2.2 factor comes from the RC time constant — it takes about 2.2τ for the gate voltage to reach 90% of the drive voltage. Ciss is the input capacitance (Cgs + Cgd) listed on the MOSFET datasheet. The MOSFET Threshold Voltage Calculator determines the voltage at which the MOSFET begins to conduct — the gate voltage must reach this level before any drain current flows.

Example: Small-Signal MOSFET (1 nF)

Vdrive = 12 V, Ciss = 1 nF, RG = 10 Ω

ton = 2.2 × 10 × 1n = 22 ns

Ipeak = 12 / 10 = 1.2 A

Qg = 1n × 12 = 12 nC

P @ 25 kHz = 12n × 12 × 25k = 3.6 mW

22 ns turn-on is fast — good for efficiency but may cause ringing. Increase RG to 22 Ω for 48 ns turn-on with less EMI.

Example: Power MOSFET (10 nF)

Vdrive = 15 V, Ciss = 10 nF, RG = 4.7 Ω

ton = 2.2 × 4.7 × 10n = 103 ns

Ipeak = 15 / 4.7 = 3.19 A

Qg = 10n × 15 = 150 nC

P @ 100 kHz = 150n × 15 × 100k = 225 mW

At 100 kHz switching, gate drive power alone is 225 mW. The gate driver IC must source 3.19 A peak. Ensure the driver can handle this — a dedicated gate driver like the MCP1407 or IR2110 is typically needed for power MOSFETs.

Speed vs EMI Trade-Off

Smaller RG means faster switching, lower switching losses, but more EMI and voltage ringing. Larger RG means slower switching, higher losses, but cleaner waveforms. Start with 10 Ω and adjust: if you see ringing on the drain waveform, increase RG. If switching losses are too high (MOSFET runs hot), decrease RG. The Transistor Base Resistor Calculator handles the analogous problem for BJT switches where the base resistor controls turn-on speed.

Split Gate Resistors

Many designs use separate resistors for turn-on and turn-off, connected via diodes. A small resistor (2–5 Ω) for turn-on gives fast switching, while a larger resistor (10–47 Ω) for turn-off controls the dV/dt to prevent false turn-on of the complementary MOSFET in a half-bridge. The Op-Amp Gain Calculator can help design an active gate driver with variable drive strength.

Frequently Asked Questions

Why use a gate resistor?
To control turn-on speed and limit peak current from the gate driver. Without it, the gate charges as fast as the driver can deliver current, causing voltage ringing, EMI, and potential damage from overshoot above the gate oxide rating.
How do I choose the value?
Start with 10 Ω. Increase if you see ringing or EMI problems. Decrease if switching losses are too high. The turn-on time is approximately 2.2 × RG × Ciss.
What is Ciss?
The MOSFET input capacitance: Cgs + Cgd. Found on the datasheet. Small-signal MOSFETs: 100–1000 pF. Power MOSFETs: 1–10 nF. High-current IGBTs: 10–50 nF.
What about separate on/off resistors?
Use a smaller resistor for fast turn-on and a larger one for controlled turn-off, connected through diodes. This is standard practice in half-bridge designs to prevent shoot-through. The BJT Gain Calculator is relevant if a BJT totem-pole driver is used instead of a dedicated gate driver IC.
Does gate drive power matter?
At low frequencies (below 10 kHz), gate drive power is negligible. Above 100 kHz with large MOSFETs, it can be significant — hundreds of milliwatts. The gate driver IC must handle both the peak current and the average power. The 555 Timer Calculator can design a simple low-frequency gate drive oscillator for testing.
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Last updated: March 2026