SNR Calculator

Compute Signal-to-Noise Ratio in dB and linear ratio from power or voltage. Includes Show Work and optional bandwidth + thermal noise helper.

How to Use

  1. Select Power or Voltage/Amplitude mode.
  2. Enter Signal and Noise values (units are handled by the dropdowns).
  3. Read SNR in dB and linear ratio.
  4. Open Show Work to see the exact formulas and steps.
SNR Readout
Updates live as you type (no URL changes).
SNR (dB)
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Linear
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Mode
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Quality: —
Tip: For power ratios use 10·log10(S/N). For voltage/amplitude use 20·log10(S/N).
Inputs & Settings
Enter Signal and Noise. Choose Power or Voltage mode. Optional: compute thermal noise from bandwidth.
If you pick Ratio, enter S as a plain number (e.g., 2).
Noise must be > 0 to compute SNR.
Optional: Thermal noise from bandwidth (kTB)
Used for kTB (Boltzmann). Default will be 290 K if blank.
Example: 20 kHz audio, 200 kHz IF, 10 MHz channel.
Thermal noise power (W)
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This is an ideal noise floor estimate (k·T·B). Tool JS will compute and optionally use it as Noise if you choose.
Show Work (step-by-step)
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Work is shown using base ratios. Power-mode uses 10·log10(·). Voltage-mode uses 20·log10(·).

SNR Reference

Definition: Signal-to-Noise Ratio compares desired signal level to noise level.

  • Power ratio (dB): SNR(dB) = 10 · log10(S / N)
  • Voltage/amplitude ratio (dB): SNR(dB) = 20 · log10(S / N)
  • Linear: SNR(linear) = S / N
Use Power mode for watts (or proportional power). Use Voltage mode for RMS voltage or amplitude ratios.

FAQ

Why is it 10·log10 for power but 20·log10 for voltage?

Power is proportional to voltage squared in many systems. Converting a squared ratio into dB doubles the multiplier.

What does 0 dB mean?

0 dB means the signal and noise levels are equal (S/N = 1).

Can SNR be negative?

Yes. Negative dB means noise is higher than signal (S/N < 1).

Tool Info

Last updated:

Updates may include UI improvements, unit support, and calculation edge-case handling.