BJT Gain Calculator
Calculate BJT DC current gain β / hFE from collector current and base current, or reverse-calculate either current from a selected gain.
This tool supports transistor characterization, amplifier analysis, bias checks, troubleshooting, and preliminary component selection using currents entered in µA, mA, or A.
Engineering tool
BJT Gain Calculator
Calculate transistor DC current gain, collector current, or base current using Ic, Ib, and β / hFE.
Collector current through the transistor output path.
Current flowing into the BJT base terminal.
DC current gain
100 β / hFE
Result console
- Collector current (Ic)
- 100mA
- Base current (Ib)
- 1mA
- DC current gain
- 100β / hFE
- Calculation type
- Calculate Gain
Formula reference
BJT Current Gain Formulas
The equations describe the ideal DC relationship between base and collector current in the forward-active region.
DC current gain: β = Ic / IbCollector current: Ic = β × IbBase current: Ib = Ic / βVariable definitions
- Ic
- collector current in amperes
- Ib
- base current in amperes
- β or hFE
- unitless DC current gain
Worked Example
Calculate Gain from Collector and Base Current
Collector current Ic = 100 mA
Base current Ib = 1 mA
β = Ic / Ib
β = 100 mA / 1 mA = 100
Engineering Notes
Gain is not constant
hFE varies widely between devices and operating conditions, even for transistors with the same part number.
Use datasheet test conditions
Datasheet hFE is normally specified at a particular collector current and collector-emitter voltage.
Switching uses forced beta
Saturated switching circuits often use a conservative forced beta instead of relying on typical hFE.
Account for temperature
Junction temperature changes transistor gain and should be included in worst-case design analysis.
Size base drive separately
For saturation switching, use the BJT Base Resistor Calculator to check base current, GPIO limits, and resistor value.
Support reference
FAQ
What is BJT current gain?
BJT DC current gain is the ratio of collector current to base current at a specified operating point. It is written as β or hFE and calculated using β = Ic / Ib.
Is β the same as hFE?
β and hFE are commonly used for the transistor's forward DC current gain. Datasheets may distinguish test notation and operating conditions, so always use the value specified for the relevant collector current and voltage.
Why does transistor gain vary?
Gain varies with device production spread, collector current, collector-emitter voltage, junction temperature, and transistor type. A single typical hFE value should not be treated as a guaranteed constant.
Can I use hFE to design a saturated switch?
Do not rely only on typical hFE for saturation switching. Use a conservative forced beta and verify base drive, VCE(sat), GPIO current, and worst-case datasheet conditions with the BJT Base Resistor Calculator.
How do I calculate base current from collector current?
Divide collector current by the selected current gain: Ib = Ic / β. For saturated switching, use the chosen forced beta rather than a typical active-region hFE.
Documentation
Related Engineering Guides
Design notes, guides, and engineering articles linked to this tool.
Engineering Guide
How to Choose and Bias a BJT Transistor
Choose and bias BJTs for switching and amplifier circuits with practical checks for base current, base resistor, forced beta, saturation, Q-point, power, thermal limits, and datasheet margin.
18 min · Intermediate
Engineering Guide
Understanding BJTs
Understand BJT fundamentals including NPN and PNP operation, cutoff, active and saturation regions, beta, base current, VBE, VCE, power dissipation, SOA, packages, and practical applications.
16 min · Beginner
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