Please enter all required numeric values.
Input Parameters Specification
TemperatureResistor temperature in Celsius. Higher temperature increases thermal agitation and noise voltage.
ResistanceResistor value in ohms. Higher resistance produces more Johnson-Nyquist noise for the same bandwidth.
BandwidthNoise bandwidth in hertz. Wider bandwidth captures more random noise energy.
Vn RMSCalculated RMS thermal noise voltage in microvolts.
Noise LevelNoise voltage converted to dBv using 20 × log10(Vn).
Use CaseHelpful for low-noise amplifier, sensor, audio, RF and measurement circuit design.
Formulas & Mathematical Logic
Step 1: Convert temperature to Kelvin: T(K) = T(°C) + 273. This gives the absolute temperature used by the thermal noise formula.
Step 2: Thermal noise voltage: Vn = √(4 × Kb × R × T × ΔF). This estimates RMS Johnson-Nyquist noise voltage.
Step 3: Microvolt conversion: Vn(µV) = Vn × 1000000. This makes very small noise values easier to read.
Step 4: Noise level: Lv = 20 × log10(Vn). This converts RMS noise voltage into dBv.
Constant: Kb = 1.3806505 × 10^-23. This is Boltzmann’s constant used in the original calculation.
Step-by-Step Example
Example values: temperature = 25 °C, resistance = 1000 Ω, bandwidth = 20000 Hz.
Convert temperature: T = 25 + 273 = 298 K.
Vn = √(4 × 1.3806505e-23 × 1000 × 298 × 20000).
Vn = 0.000000573 V = about 0.573 µV RMS.
Lv = 20 × log10(0.000000573) = about -124.84 dBv.
Practical meaning: even a simple resistor creates measurable noise, and wide bandwidth increases the total noise voltage.
About This Calculator
Estimate the tiny random voltage every resistor creates just by being warm.
This CalcBoy thermal noise calculator finds RMS noise voltage and dBv level from temperature, resistance and bandwidth.
The Thermal Noise Calculator is useful for low-noise electronics, RF receivers, audio preamps, precision sensor interfaces, measurement systems and analog circuit design. Thermal noise, also known as Johnson noise or Johnson-Nyquist noise, is created by random motion of charge carriers inside a resistor. It exists even when no signal is applied and becomes part of the circuit’s noise floor.
Best UseLow-noise amplifiers, audio circuits, RF receivers, sensor inputs and precision analog design.
Key InputsTemperature, resistance and measurement bandwidth.
Design BenefitQuickly compare resistor noise contribution before final component selection.
Practical ReminderNoise increases with resistance, temperature and bandwidth.
The calculator uses the classic thermal noise equation. Higher resistance produces more noise voltage. Higher temperature increases random carrier energy. Wider bandwidth includes more noise power, so the total RMS noise rises with the square root of bandwidth. This is why a wideband amplifier can appear noisier than a narrowband filtered system even when both use the same resistor value.
Quick tip: in sensitive circuits, reduce unnecessary bandwidth and avoid very high resistor values at critical low-noise input nodes.
For real circuit design, thermal noise is only one part of the total noise picture. Op-amp voltage noise, current noise, flicker noise, ADC quantization noise, PCB leakage, shielding, grounding and source impedance also matter. Still, resistor thermal noise is a fundamental starting point because it sets a physical lower limit that cannot be removed by better layout or cleaner power supplies.
Frequently Asked Questions
What is thermal noise?
Thermal noise is random electrical noise produced by charge carrier motion inside a resistor or conductor due to temperature.
Is thermal noise the same as Johnson noise?
Yes. Thermal noise is also called Johnson noise or Johnson-Nyquist noise.
Why does bandwidth affect noise?
Thermal noise is spread over frequency, so a wider bandwidth includes more noise power and increases RMS noise voltage.
Does a higher resistor value create more noise?
Yes. RMS thermal noise voltage increases with resistance for the same temperature and bandwidth.
Can thermal noise be completely removed?
No. It is a physical noise source, but filtering and careful circuit design can reduce how much noise appears in the signal band.
What is dBv noise level?
dBv expresses voltage level relative to 1 volt using 20 × log10(V).