What Is the HFE of 2N3904? Gain Value Explained
The HFE of 2N3904 is its DC current gain, the number that tells you how many times the transistor multiplies a tiny base current into a larger collector current. For most parts you pull from a bin, that value lands somewhere between 100 and 300. I will show you where the figure comes from, why it drifts, and how I check it in about 2 minutes.
Last updated: August 13, 2026. I rewrote this from a vague overview into a working guide with real datasheet numbers, a spec table, and a bench-test routine you can copy.
What the HFE of 2N3904 Really Means
HFE is the forward current gain of the transistor in a common-emitter setup. Older datasheets print it as hFE. Most people on the bench just call it beta. The idea behind it is short. Feed a small current into the base, and the collector passes a much bigger one. Divide the big number by the small one, and you have the gain.
Here is the whole formula. hFE equals collector current divided by base current, both taken as steady DC values. So push 0.1 mA into the base, get 20 mA at the collector, and your gain is 200. That is it. No calculus, no magic, just a ratio you can measure with parts you already own.
Figure: Off characteristics of the 2N3904.
Figure: On characteristics of the 2N3904.
The Real HFE Numbers From the Datasheet
Onsemi tests the 2N3904 at a collector-emitter voltage of 1 V, then reads the gain at several current points. The datasheet even labels the row plainly as “DC current gain hFE” so nobody misreads it. The spread is wide on purpose. A cheap part cannot promise one exact figure, so it promises a floor. I keep this table taped near my bench.
| Collector current (Ic) | Minimum hFE | What it tells you |
|---|---|---|
| 0.1 mA | 40 | gain is weak at tiny currents |
| 1 mA | 70 | still climbing |
| 10 mA | 100 to 300 | the sweet spot |
| 50 mA | 60 | starting to sag |
| 100 mA | 30 | close to the 200 mA ceiling |
Read the table top to bottom and the shape jumps out. The gain rises, peaks near 10 mA, then falls off hard as you drive the part toward its limits. Most hobby circuits sit in that happy middle band. Notice the sheet prints only a minimum for most rows. Your real part usually beats it, sometimes by a lot, which is exactly why you cannot design around one number.
Why the HFE of 2N3904 Drifts So Much
The HFE of 2N3904 is not one fixed value, and that surprises people. Two parts off the same reel can differ wildly. The datasheet lets the gain spread more than 30% from unit to unit, and often much more than that. Temperature piles on. Warm the junction and the gain can climb 50% or higher. Cool it down and it sags again.
This is why no careful designer leans on a single hFE reading. Don’t trust one meter number and build a whole amplifier on it. You design so the circuit still works whether the part shows up at 100 or at 300. The base resistor sets the current. The gain only has to be enough to do the job.
There is a deeper reason the base current stays so small, and I walked through the physics in a separate piece on why the base current stays weaker than the collector current. If you have ever cooked a part by wiring it in backwards, what happens when you reverse a transistor’s polarity is worth five minutes too. And when low noise matters in your design, I dug into why bipolar parts can hiss more than you expect.
How I Measure the HFE of 2N3904 on the Bench
You do not need a lab analyzer for this. A cheap multimeter with an hFE socket gets you close, and a resistor jig gets you the honest figure. Here is my routine.
- Set the meter to its hFE mode and pick the NPN slot.
- Push the transistor legs into the E, B, C holes. Mind the pinout. With the flat face toward you, the legs read E, B, C from left to right.
- Read the number. A healthy part shows something from 100 to 300.
- For a real test, build a quick jig. Feed a known base current through a resistor and measure the collector current with the part biased near 1 V.
- Divide collector current by base current. That result is your gain.
The socket method is fast, roughly 2 minutes, but it tests at a low current the meter picks for you. The jig is slower and honest. I’d recommend the jig whenever the exact number actually drives your design.
Quick facts worth keeping in your head:
- NPN bipolar junction transistor in a TO-92 case
- Collector current up to 200 mA
- Collector-emitter voltage up to 40 V
- Power dissipation around 625 mW at room temperature
- On the market for over 40 years and still in every parts bin
When the Gain Actually Matters
Not every circuit cares about beta. In a switch, you just need enough gain to saturate. Drive the base hard and forget the exact figure. In a linear amplifier the story flips, because gain sets your bias point, so a 3-to-1 spread forces you to add feedback. An emitter resistor fixes most of it. The trick is to design for the whole range, not for one lucky part. Do that, and the circuit behaves whether your transistor is a runt or a champion.
Frequently Asked Questions
What is a good HFE value for the 2N3904?
Anything from 100 to 300 at 10 mA is normal and healthy. If a socket reading drops under 40, the part is either damaged or wired into the wrong pins.
Is a higher HFE always better?
Not really. High gain sounds great, but it brings more part-to-part variation and a bit more noise. For a switch you only need enough to saturate. For an amplifier, stable beats high every time.
Does temperature change the HFE of the 2N3904?
Yes. Warm the junction and the gain climbs, often by 50% or more across the rated range, because the carrier conductivity in the semiconductor shifts. Good designs use feedback instead of trusting one figure.
Can I test HFE with a normal multimeter?
Yes, if it has an hFE socket. It is quick and fine for sorting parts. For a true figure at your working current, build a small resistor jig and do the division yourself.
Why do two 2N3904 parts read different gains?
Manufacturing spread. The process cannot hold beta tight, so the datasheet only promises a minimum. A 30% gap between two parts off the same reel is completely normal.
Related Reading
Bottom Line
The HFE of 2N3904 sits between 100 and 300 for most parts, peaks near 10 mA, and drifts hard with both temperature and manufacturing spread. Treat the HFE of 2N3904 as a range, not a promise. Design so your circuit works across that whole band, add an emitter resistor when gain matters, and a low-beta part will never bite you.