SNR Calculator (power, voltage, dB)

Understanding the signal-to-noise ratio calculator — concept and principle

Signal-to-noise ratio (SNR) compares the strength of a wanted signal with the background noise that accompanies it. It is quoted in decibels for audio equipment, radio links, sensors, imaging and data converters. This calculator converts a signal and a noise measurement in the same unit into SNR in dB, using the power formula or the voltage formula depending on what you measured.

A signal 1,000 times stronger than the noise (in power) is 30 dB above it.

How it is calculated

Power quantities (watts, milliwatts): SNR = 10 × log₁₀(P_s / P_n).
Voltage or other amplitude quantities (RMS volts): SNR = 20 × log₁₀(V_s / V_n).

Both inputs must use the same unit, and for voltages they should be RMS values measured across the same impedance.

The principle

The decibel is a logarithmic way of expressing a power ratio: one bel is a factor of ten in power, and a decibel is a tenth of a bel, hence the factor 10. Power is proportional to the square of voltage (P = V²/R), and log(V²) = 2 log V, so the same ratio expressed in voltages needs a factor of 20. That is why a 30 dB SNR means the signal has 1,000 times the noise power but only about 31.6 times the noise voltage. Logarithms also let gains and losses along a chain be added instead of multiplied.

Worked example

Inputs: signal = 1, noise = 0.001, units = power.
Ratio: 1 / 0.001 = 1,000.
log₁₀(1,000) = 3.
SNR = 10 × 3 = 30 dB.

If the same numbers were RMS voltages, the result would be 20 × 3 = 60 dB.

Each point is the calculator re-run with only “Noise (same unit)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Noise (same unit)	SNR (dB)
0.00025	36.02059991
0.0005	33.01029996
0.00075	31.24938737
0.001	30
0.00125	29.03089987
0.0015	28.23908741
0.002	26.98970004

How to read the result

Higher is better. Each 10 dB is another factor of ten in power. As rough orientation, 0 dB means signal and noise are equally strong; around 20–30 dB speech is intelligible but noise is obvious; good consumer audio equipment is usually specified in the region of 90 dB or more; an ideal 16-bit converter reaches about 98 dB. In digital communications the SNR needed depends on the modulation scheme and the acceptable error rate.

Common mistakes

Using 10·log for voltages or 20·log for powers, which halves or doubles the answer.
Comparing specifications measured with different weightings (A-weighted vs unweighted) or bandwidths.
Measuring noise with the signal still present, which mixes distortion into the noise figure.
Entering peak values for one input and RMS for the other.

Keep in mind: SNR from a single pair of numbers ignores frequency content, bandwidth and distortion. Manufacturer figures depend on test conditions, so compare them only when the measurement method is stated and equal.

Frequently asked questions

Can SNR be negative?

Yes. A negative value means the noise is stronger than the signal; GPS and some spread-spectrum systems routinely work below 0 dB thanks to processing gain.

What is the difference between SNR and SINAD?

SINAD counts noise plus distortion in the denominator, so it is never higher than SNR for the same device.

How do I add noise from two independent sources?

Add their powers, not their decibel values. Two equal uncorrelated noise sources raise the noise by about 3 dB.

Sources: IEC 60027-3, Letter symbols to be used in electrical technology — Logarithmic and related quantities, and their units · Audio Engineering Society, AES17 Standard method for digital audio engineering — Measurement of digital audio equipment

Checked 8 Nov 2026. Standard textbook formulas in SI units, computed in your browser. For learning and estimates — real designs must follow your local codes and be checked by a qualified engineer.

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