How to Use MOSFET Calculator
The MOSFET Calculator helps you quickly characterise a MOSFET’s operating point from its terminal voltages and device parameters.
- Select channel type — Choose N-Channel or P-Channel.
- Enter VG, VS, VD — Provide the gate, source, and drain voltages in volts. The calculator automatically computes VGS and VDS.
- Enter Vth — The threshold voltage determines whether the device is on or off.
- Enter k (optional) — Providing the transconductance parameter (A/V²) lets the MOSFET Calculator compute the drain current ID for the detected region.
- Override ID or VDS (optional) — If you already know ID from measurement, enter it to enable power and RDS(on) calculations. You can also override VDS for the RDS(on) calculation.
- Read the results — The calculator shows the operating region, VGS, VDS, ID (if computable), power dissipation, and RDS(on).
Formula & Theory — MOSFET Calculator
The MOSFET Calculator implements the standard square-law MOSFET model:
Terminal Voltages
VGS = VG − VS
VDS = VD − VSOperating Region (N-Channel)
| Condition | Region |
|---|---|
| VGS ≤ Vth | Cutoff |
| VGS > Vth and VDS < VGS − Vth | Linear (Ohmic) |
| VGS > Vth and VDS ≥ VGS − Vth | Saturation |
Drain Current
Cutoff:
ID = 0Linear / Ohmic:
ID ≈ k × [(VGS − Vth) × VDS − VDS² / 2]Saturation:
ID ≈ 0.5 × k × (VGS − Vth)²Power and On-Resistance
P = VDS × ID
RDS(on) ≈ VDS / ID| Symbol | Meaning |
|---|---|
| k | Transconductance parameter (A/V²) = μₙCₒₓ(W/L) |
| Vth | Threshold voltage (V) |
| VGS | Gate-source voltage (V) |
| VDS | Drain-source voltage (V) |
| ID | Drain current (A) |
| P | Power dissipation (W) |
| RDS(on) | On-state drain-source resistance (Ω) |
For P-channel MOSFETs, all polarities are reversed; the MOSFET Calculator applies the appropriate sign convention automatically.
Use Cases for MOSFET Calculator
The MOSFET Calculator is useful across electronics, physics, and hardware design:
- Circuit design verification — Quickly confirm whether a MOSFET is biased in the correct region for a given application — saturation for switching, linear for amplification.
- Power electronics — Compute RDS(on) and power dissipation for a power MOSFET switch to evaluate thermal performance and efficiency.
- Electronics education — Students learning semiconductor device physics use the MOSFET Calculator to build intuition about threshold voltage, transconductance, and operating regions.
- Amplifier design — Determine the quiescent drain current and power consumption for a common-source amplifier stage by entering the bias voltages and device k parameter.
- Simulation cross-check — Use the MOSFET Calculator to quickly sanity-check SPICE simulation results before spending time on full-circuit simulation.
- Hardware prototyping — Embedded engineers select MOSFETs for motor drivers or power supplies by computing the expected RDS(on) and dissipation under worst-case conditions.