Every resistor hisses: its electrons jiggle with thermal energy, producing a small random voltage. It sets the ultimate noise floor of audio preamps, radio receivers and sensors – which is why low-noise designs use low resistances or cool their circuits.
How to use the Resistor Noise Calculator
- Resistance R
- Temperature
- Bandwidth Δf
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the resistance, the temperature and the bandwidth.
Inputs explained
| Field | What to enter |
|---|---|
| Resistance R | Units: kΩ, Ω, MΩ |
| Temperature | Units: K, °C, °F |
| Bandwidth Δf | Units: kHz, Hz, MHz |
What each result means
- Noise voltage (RMS) = sqrt(4×1.380649e-23×[Temperature]×[Resistance R]×[Bandwidth Δf])
- Noise density = sqrt(4×1.380649e-23×[Temperature]×[Resistance R])×1e9
- Level in dBu = 20×log10([Noise voltage (RMS)]÷0.7746)
- Level in dBV = 20×log10([Noise voltage (RMS)])
Example values
How the main result changes when Resistance R changes and everything else stays at the example values above:
| Resistance R (kΩ) | Noise voltage (RMS) (µV) |
|---|---|
| 5 | 1.2872 |
| 7.5 | 1.5764 |
| 10 | 1.8203 |
| 12.5 | 2.0352 |
| 15 | 2.2294 |
| 20 | 2.5743 |
Formula
V_n = √(4·k_B·T·R·Δf)
Worked example
Inputs — Resistance R: 10 kΩ; Temperature: 300 K; Bandwidth Δf: 20 kHz.
Results — Noise voltage (RMS) = 1.82032 µV; Noise density = 12.87159 nV/√Hz; Level in dBu = -112.579 dBu; Level in dBV = -114.797 dBV.
Key terms
- Johnson–Nyquist noise
- Thermal noise from charge carriers in a resistor.
Frequently asked questions
What is the noise of a 1 kΩ resistor?
About 4 nV/√Hz at room temperature.
Can noise be avoided?
Only by lowering resistance, temperature or bandwidth.
Is all resistor noise thermal?
No – excess (current) noise depends on construction; metal film is best.
Why does bandwidth matter?
Noise power is spread evenly across frequency.