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MOSFET Conduction Loss Calculator

Calculate MOSFET conduction loss from I, Rds(on), current definition (DC / on-interval RMS / full-cycle RMS), and optional Rds(Tj) via linear α or datasheet ratio. Runs locally in your browser.

Instant result
Result
—

Enter values to calculate.

Inputs—
Mode—
Formula—
Trust summary CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance
Input interpretation
Enter values to calculate.
Result
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Assurance
Engineering
Declared partition coverage
PASS · 4/4 declared partitions (dc, on_interval_rms, full_cycle_rms, invalid-domain) · Matrix
Known limitations
  • Conduction only — switching/Coss/Qrr excluded; temperature none in this CVP wave goldens
  • Core CVP does not include live graph, viewport, or pointer interaction.
Model
MOSFET conduction loss and resistive VDS estimate from I, Rds(on) at Tref, current_basis, duty D when it applies, and optional Rds(Tj).
Scope
Constant Rds during on-time at the applied Rds_Tj.
Verification
Engine tested · Source checked · v1.2.2 · CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance· View Manifest · CVP overview · Specification
Versions
Calculation 1.2.2 · CVP protocol 1.0.0-proposed
CVP identity
8/8 property · digest 77fa2f728b57
Legacy regression
32/32 tests · Production surface contract 12/12
Reference
O1 model · O2 expected_values · O2 numerical_behavior
Interfaces
PASS · UI (SSR) / REST / MCP — ui-ssr is query-result HTML, not a live browser session.
Supplemental domain review
Internal · Pass · electrical-engineer · 2026-08-14
Named expert review
Not performed
CVP suite
3/3 golden · 13/13 CVP boundary · 13/13 invalid · 8/8 property · 2/2 cross-interface · 12/12 CVP contract · Manifest
Sources
Sources
Evidence
7 legacy golden · 13 legacy boundary · legacy regression suite · 3/3 oracle-backed golden · 13/13 invalid · Artifact integrity PASS · CalculatorX electrical review (EE-001)
This calculator CURRENT · Public schema 1.2.2 matches · Semantic contract ✓ · Production attested · Public/cache ✓ · Origin ✓
Semantic contract
PASS
Full verification

Manifest identity, reference classes, interfaces, suite, and production records.

Formulas

Core equations used by this calculator.

On-interval RMSP = I_on,rms² × Rds(on) × D
Full-cycle MOSFET RMS / DCP = I_rms² × Rds(on)
Resistive drop at entered currentVDS estimate = I × Rds_Tj
Linear Rds(Tj)Rds(Tj) = Rds(Tref) × (1 + α × (Tj − Tref))
Datasheet ratioRds(Tj) = Rds(Tref) × rds_ratio
icurrent_basis is required and selects the I definition — the engine will not guess a waveform factor. temperature_model (none / ratio / linear) selects whether Rds is used as entered or scaled to Tj. Prefer a datasheet Rds(Tj)/Rds(Tref) ratio; default α = 0.006 /°C is a Si MOSFET planning default — not a datasheet coefficient. Switching loss is out of scope.

How to use

1

Choose the current definition

DC for continuous conduction. On-interval RMS if I is the current while the FET is on. Full-cycle MOSFET RMS if I already includes off-time (typical datasheet / vendor I_RMS).

2

Enter current I and Rds(on)

Enter datasheet Rds(on) at Tref (usually 25 °C) and your Vgs. Optionally open Advanced to scale to junction temperature.

3

Enter duty D only for on-interval RMS

D = ton/T. Hidden for DC and full-cycle RMS so duty cannot be double-counted.

4

Optional — Rds(Tj)

Linear: Rds·(1+α·(Tj−Tref)) with planning default α=0.006 /°C. Ratio: paste Rds(Tj)/Rds(Tref) from the datasheet curve.

Example calculations

Common configurations with formula and result.

ϟ

DC 10 A · 50 mΩ

current_basis = dc · I = 10 A · Rds = 0.05 Ω

P = I² × Rds
P = 5 W · VDS estimate = 0.5 V
ϟ

On-interval PWM 50%

Same 10 A on-state RMS · D = 0.5

P = I² × Rds × D
P = 2.5 W
ϟ

Full-cycle RMS of the same PWM

I_mos,rms = 10√0.5 ≈ 7.071 A · current_basis = full_cycle_rms

P = I_rms² × Rds
P = 2.5 W (same waveform; do not also enter D = 0.5)
ϟ

Hot 100 °C · ratio 1.44

Same 10 A DC · 50 mΩ @ 25 °C · rds_ratio = 1.44

Rds_Tj = 50 mΩ × 1.44
P @ 25 °C = 5 W · P @ Tj = 7.2 W · VDS estimate = 0.72 V

Illustrative conduction loss

Common values at a glance.

current_basisIRds(on)DP_cond
dc10 A50 mΩ15 W
on_interval_rms10 A50 mΩ0.52.5 W
full_cycle_rms7.071 A50 mΩ—2.5 W
dc + ratio 1.4410 A50→72 mΩ17.2 W
i Does not include switching or reverse-recovery loss. The 7.071 A row is the period RMS of the 10 A / D=0.5 rectangle. 72 mΩ is 50 mΩ × 1.44 (datasheet-style hot ratio).

MOSFET Conduction Loss calculator specification

Version 1.2.2 · Engine tested · Supplemental domain review · Internal · 2026-08-14

Calculation status

Review policy · Evidence · Reviewed by CalculatorX electrical review (EE-001) (electrical-engineer)

Definition
MOSFET conduction loss is the average power dissipated in Rds(on) at the applied temperature. If I is RMS during the ON interval, P = I_on,rms² · Rds_Tj · D. If I is MOSFET RMS over the full period, P = I_mos,rms² · Rds_Tj and D must not be applied again. DC is the D = 1 case. Rds_Tj may be the entered Rds, a linear α·ΔT scale, or a datasheet ratio.
What it calculates
MOSFET conduction loss and resistive VDS estimate from I, Rds(on) at Tref, current_basis, duty D when it applies, and optional Rds(Tj).
Inputs
  • I > 0 (A) — current; meaning set by current_basis
  • Rds > 0 (Ω) — on-resistance at Tref in SI ohms
  • current_basis — required: dc | on_interval_rms | full_cycle_rms. The engine will not infer what I means.
  • D optional in (0, 1] — used only for on_interval_rms; default 1
  • temperature_model — none (default) | linear | ratio; omitted infers ratio if rds_ratio is set (ratio wins even when Tj_C/alpha_per_C are also present), else linear if Tj_C or alpha_per_C is set, else none
  • Tj_C — required for linear
  • Tref_C — default 25
  • alpha_per_C — linear coefficient; default 0.006 /°C (Si planning default) with warning RDS_TEMP_COEFF_DEFAULT
  • rds_ratio > 0 — required for ratio; datasheet Rds(Tj)/Rds(Tref)
Outputs
  • P_W — conduction loss at Rds_Tj (W)
  • V_drop — I·Rds_Tj at entered current (V)
  • Rds_Tj — Rds used in P_W (equals Rds when temperature_model=none)
  • P_W_ref, V_drop_ref — Tref comparison when a temperature model is applied
  • Echoed I, Rds, D, current_basis, temperature_model, rds_ratio
Formula
on_interval_rms: P_W = I² × Rds_Tj × D; dc and full_cycle_rms: P_W = I² × Rds_Tj; V_drop = I × Rds_Tj; linear Rds_Tj = Rds·(1+α·(Tj−Tref)); ratio Rds_Tj = Rds·rds_ratio
Assumptions
  • Constant Rds during on-time at the applied Rds_Tj.
  • current_basis is the contract for what I means; the engine will not guess a waveform factor.
  • No switching, Coss, or gate-drive loss.
  • Rds(Tj) is first-order linear or a datasheet ratio — not a physics compact model.
  • Default α = 0.006 /°C is a Si MOSFET planning default, not manufacturer validated.
Units
  • A, Ω, °C → W, V
Boundary conditions
  • Missing I/Rds/current_basis → MISSING_REQUIRED_INPUT
  • ≤ 0 → VALUE_MUST_BE_POSITIVE
  • Non-finite → INVALID_NUMBER
  • D not in (0, 1] → FRACTION_OUT_OF_RANGE
  • Unknown current_basis or temperature_model → INVALID_MODE
  • linear without Tj_C, or ratio without rds_ratio → MISSING_REQUIRED_INPUT
  • D supplied with dc or full_cycle_rms → warning DUTY_NOT_APPLICABLE; D not applied
  • Explicit none with Tj/α/ratio present → warning TEMPERATURE_NOT_APPLIED
  • linear with omitted α → warning RDS_TEMP_COEFF_DEFAULT (α=0.006 /°C)
  • ratio with α also supplied → warning ALPHA_IGNORED_WHEN_RATIO
  • Rds(Tj)/Rds(Tref) outside 0.5–2.5 → warning RDS_TEMP_FACTOR_OUTSIDE_TYPICAL
Example
current_basis=dc, I=10, Rds=0.05, rds_ratio=1.44 → P_W=7.2, Rds_Tj=0.072, P_W_ref=5
Validation cases

9 published on this page · 32/32 tests · Production surface contract 12/12 · View evidence

  • current_basis=dc, I=10, Rds=0.05 → P_W=5, V_drop=0.5, D=1, temperature_model=none
  • current_basis=on_interval_rms, I=10, Rds=0.05, D=0.5 → P_W=2.5
  • current_basis=full_cycle_rms, I=7.0710678118654755, Rds=0.05 → P_W=2.5
  • current_basis=full_cycle_rms, I=7.0710678118654755, Rds=0.05, D=0.5 → P_W=2.5 (D ignored)
  • current_basis=dc, I=10, Rds=0.05, rds_ratio=1.44 → P_W=7.2, Rds_Tj=0.072, P_W_ref=5
  • current_basis=dc, I=10, Rds=0.05, temperature_model=linear, Tj_C=100, alpha_per_C=0.006 → P_W=7.25, Rds_Tj=0.0725
  • I=10, Rds=0.05 (no current_basis) → error MISSING_REQUIRED_INPUT
  • current_basis=peak → error INVALID_MODE
  • current_basis=dc, temperature_model=arrhenius → error INVALID_MODE
Sources
  • IEC 60747-8 — Semiconductor devices — Discrete devices — Part 8: Field-effect transistors — Drain-source on-state resistance RDS(on)
    Supports: RDS(on) as the on-state resistance used in conduction-loss estimates
  • Infineon — OptiMOS device selection for synchronous rectification — Conduction losses P_cond = I_RMS² × RDS(on) · accessed 2026-08-14
    Supports: Vendor conduction-loss model using MOSFET RMS current (not converter output current) without an extra duty factor
  • Texas Instruments SSZTB57 — How to Minimize MOSFET Conduction Loss in Battery-Powered Applications — P_cond = I_RMS² × RDS(on) · accessed 2026-08-14
    Supports: Official TI conduction-loss formula using MOSFET RMS current
  • Erickson & Maksimović — Fundamentals of Power Electronics — Conduction loss in semiconductor switches
    Supports: I_rms of the switch current over the period; equivalent to on-interval RMS × √D for rectangular current
  • NIST Guide to the SI (SP 811) — SI units for current, resistance, and power · accessed 2026-08-14
    Supports: A, Ω, W relationships
Last reviewed
2026-08-14
Reviewed by
CalculatorX electrical review (EE-001) (electrical-engineer)
Calculation version
1.2.2

Background

Interpretation and common distinctions.

Calculate MOSFET conduction loss with an explicit current-basis contract so RMS current and duty cycle are not double-counted, plus an optional Rds(Tj) correction.

Default example: DC 10 A · 50 mΩ @ 25 °C → P = 5 W, VDS estimate = 0.5 V.

Same rectangular PWM, two correct inputs:

  • On-interval RMS 10 A, D = 0.5 → 2.5 W
  • Full-cycle MOSFET RMS 10√0.5 ≈ 7.071 A → 2.5 W

Entering 7.071 A and D = 0.5 as if both applied would understate loss (1.25 W). Full-cycle RMS ignores D.

Hot Rds example: same 10 A DC · 50 mΩ @ 25 °C · datasheet ratio 1.44 → Rds_Tj = 72 mΩ → P @ Tj = 7.2 W (P @ 25 °C remains 5 W). Linear α = 0.006 /°C at 100 °C gives 72.5 mΩ / 7.25 W.

Supported and not supported

Supported

  • current_basis: dc | on_interval_rms | full_cycle_rms
  • temperature_model: none | linear | ratio
  • Conduction loss and resistive VDS estimate at Rds_Tj
  • API / MCP via electrical.mosfet.conduction_loss

Not supported

  • Switching loss / Eon·Eoff
  • Physics compact models or manufacturer-validated α
  • Body-diode reverse recovery
  • Parallel FET current sharing
  • Waveform-factor inference from peak / average current

Agent / API notes

Capability id: electrical.mosfet.conduction_loss · tool id: mosfet-conduction-loss · pin calculation_version: 1.2.2.

current_basis is required (v1.2.1+). Omitting it returns MISSING_REQUIRED_INPUT — the engine will not guess whether I is DC, ON-interval RMS, or full-cycle MOSFET RMS. Input/output schemas are generated from the same required list and calculation_version. Share URLs store canonical Rds in ohms; display milliohms are UI state.

Omitting temperature_model infers ratio if rds_ratio is set (ratio wins even when Tj_C or alpha_per_C is also present), else linear if Tj_C or alpha_per_C is set, else none. Prefer sending temperature_model=ratio with a datasheet rds_ratio over the linear planning α.

Stable error codes: MISSING_REQUIRED_INPUT, INVALID_NUMBER, VALUE_MUST_BE_POSITIVE, FRACTION_OUT_OF_RANGE, INVALID_MODE.

Warning codes: DUTY_NOT_APPLICABLE, VDS_AT_ENTERED_CURRENT, TEMPERATURE_NOT_APPLIED, RDS_TEMP_COEFF_DEFAULT, ALPHA_IGNORED_WHEN_RATIO, RDS_TEMP_FACTOR_OUTSIDE_TYPICAL.

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Frequently asked questions

Key distinctions behind the calculation.

What is MOSFET conduction loss?

Average power lost to Rds(on) while the FET conducts. Switching, Coss, gate-drive, and reverse-recovery losses are separate.

Should I use peak, on-interval RMS, or full-cycle RMS?

Never use peak alone. If I is RMS during the ON interval, choose on-interval RMS and enter D. If I is the MOSFET current RMS over the whole period (the usual vendor I_RMS), choose full-cycle MOSFET RMS and do not enter D — P = I_rms² · Rds. Mixing full-cycle RMS with D understates loss by about D (½ at 50% duty).

What is duty cycle D?

D = ton/T, the fraction of the period the device is on (0 < D ≤ 1). It is applied only for on-interval RMS. For DC and full-cycle RMS the calculator forces D = 1 in the power formula.

Why is VDS estimate not always VDS(on)?

The calculator reports I × Rds at the current you entered. For DC that is the on-state drop. For an RMS current it is a resistive drop at that RMS value, not a particular instant of vDS(t).

Does this include temperature effects on Rds?

Optionally. Leave temperature_model at none to use Rds as entered. Prefer Datasheet ratio (Recommended): Rds·rds_ratio from the normalized Rds(on) vs Tj curve. Linear estimate is a planning approximation Rds·(1+α·(Tj−Tref)); default α=0.006 /°C is a Si planning default, not manufacturer validated. The primary result is P at Rds_Tj; P at Tref is shown for comparison.

What if I, Rds, or current_basis is missing or zero?

The calculator and API reject the request with MISSING_REQUIRED_INPUT or VALUE_MUST_BE_POSITIVE. From v1.2.1, current_basis is required — the engine will not guess what I means. Unknown current_basis or temperature_model returns INVALID_MODE. linear without Tj_C and ratio without rds_ratio also return MISSING_REQUIRED_INPUT.

Is switching loss included?

No. This probe is conduction only. Use MOSFET Total Loss to compose conduction + switching + gate + Coss + Qrr, or the MOSFET Switching Loss calculator for the hard-switching term alone.