BJT h-Parameters Calculator

Compute BJT small-signal hybrid parameters (hie, hfe, hre, hoe) from bias point and beta. The classic 4-terminal model used in textbook amplifier analysis.

Calculator Electronics Updated Apr 23, 2026
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How to Use
  1. Enter DC bias point: collector current Ic, beta (hfe), and Early voltage Va.
  2. Tool computes hie (input Z), hfe (current gain), hoe (output admittance), and hre (reverse voltage transfer — usually negligible).
Input
mA
V
°C
Presets
H-Parameters
hie
—Ω
hfe
—
hoe
—µS
gm = hfe/hie
—mS

Show Work

Enter values.

Formulas

hie
hie ≈ hfe · Vt / Ic
Input Z, Vt = kT/q ≈ 25.85 mV @ 300 K
hfe
β (datasheet)
Current gain.
hoe
hoe ≈ Ic / Va
Output admittance.
hre
< 10⁻⁴
Usually ignored.
gm (pi model)
gm = Ic / Vt = hfe/hie
Transconductance.
ro
ro = 1/hoe = Va/Ic
Output resistance.

History of h-Parameters

The hybrid (h) two-port parameter set was standardized by the IRE (now IEEE) in 1956 as the preferred small-signal characterization for BJTs. The h-parameters mix voltage and current variables (hence 'hybrid') because they match BJT behavior better than pure Z or Y parameters. By the 1990s SPICE-era design had largely shifted to the pi-model (r_pi, gm, ro), but h-parameters still appear in datasheets and textbooks as the standard characterization.

About This Calculator

Enter bias current Ic, beta (datasheet typical), Early voltage Va (typically 50-150 V for signal BJTs), and temperature. The tool computes h-parameters using Vt = kT/q (26 mV at 300 K), hie = β·Vt/Ic, hoe = Ic/Va, and equivalent pi-model gm, rπ, ro.

These are small-signal AC parameters — valid at a specific bias point. For large-signal analysis (switching, power stages), use the Ebers-Moll or Gummel-Poon SPICE model instead. Everything runs client-side.

Frequently Asked Questions

What are h-parameters?

Hybrid 2-port parameters: V_be = hie·Ib + hre·Vce; Ic = hfe·Ib + hoe·Vce. The "hybrid" means mixed V and I variables — more intuitive than pure-Z or pure-Y parameter sets for BJT characterization.

Still used?

SPICE uses pi-model (rπ, gm, ro) instead, but h-parameters are still standard in textbooks and datasheets. Converting: rπ = hie, gm = hfe/hie, ro = 1/hoe.

Temperature effects?

hie ≈ 26mV/Ib at room temp; scales inversely with Ic. hfe rises ~0.5%/°C, Va rises slightly with temperature. hre is usually &lt; 10⁻⁴, ignorable for most designs.

Common Use Cases

CE Amp Analysis

Hand-analysis of common-emitter gain: A = -hfe·R_L/(hie + (1+hfe)·R_E).

Input/Output Z

Z_in = hie (common-emitter); Z_out ≈ 1/hoe (high impedance in CE).

Compare to pi

Verify SPICE pi-model parameters (rπ, gm, ro) against h-parameter equivalents.

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