MOSFET Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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Electrical results can look precise while a unit, operating mode, or component assumption quietly changes the answer. MOSFET Calculator keeps the calculation tied to the quantities on this page, so you can trace the displayed drain current back to the values you entered rather than treating it as a black-box number.

What this calculator does

The MOSFET Calculator turns Threshold voltage (VT), K parameter, Drain-source voltage (Vds), Gate-source voltage (Vgs) into the page’s Drain current using the circuit or component relationship below. Where the page shows supporting quantities, they come from the same idealized model so you can cross-check the headline rather than reading one isolated number.

How to use it

Start with the fields that actually drive this result: Threshold voltage (VT), K parameter, Drain-source voltage (Vds), Gate-source voltage (Vgs). Keep units consistent with the menus beside the fields and avoid mixing values measured under different conditions. After calculating, change one input at a time if you are comparing scenarios; that makes cause-and-effect much easier to see.

How the calculation works

The page uses a simplified square-law MOSFET model. With overdrive Vov = Vgs − VT, cutoff applies when Vov ≤ 0; the triode expression is k(2VovVds − Vds²) when Vds < Vov, and saturation uses Id = kVov². Power is |Id·Vds|.

Example

Using the page’s default example (Threshold voltage (VT) = 2 V; K parameter = 1 mA/V²; Drain-source voltage (Vds) = 5 V; Gate-source voltage (Vgs) = 4 V), the calculator reports Drain current of 0.004 A. Change one driving input at a time and confirm the result moves in the direction predicted by the equation; that is a quick way to catch a unit or mode mistake.

How to interpret the result

Interpret the Drain current as an idealized circuit/component quantity for the exact mode and units entered. Use it to compare designs or check hand calculations, but keep component tolerances, ratings, frequency dependence, and real operating conditions in view before turning the number into a hardware decision.

Limitations and notes

This square-law model is intentionally simple and does not represent a modern MOSFET over its full operating range. RDS(on), channel-length modulation, temperature, capacitances, SOA, switching loss, and package thermal limits are outside the calculation.