# Signal-to-Noise (SNR) Ratio calculator

This Signal-to-Noise Ratio calculator converts signal and noise voltage levels to a deciBel (dB) ratio. To use this tool simply enter the levels and select the appropriate units.

## Formula

SNR (dB) = 20*Log10(S/N)

Note that since the signal and noise values are represented as voltage levels, there’s a square or 20*Log relationship to convert to power ratio.

## Example Calculations

• If the signal and noise voltage levels are the same, the SNR is 0 dB
• For a signal level of 9V and Noise level of 3V, the SNR is 9.54 dB

## Can SNR be negative?

Yes, SNR can be a negative value. This is the case when the noise is greater than the signal. Practically this means that the signal is buried in the noise. A related question is:

Can the signal be detected if the SNR is negative?

The answer is Yes. Use this calculator to see that with 10 MHz of bandwidth and an SNR value of -10 dB, a throughput of over 1 Mbps cane be achieved.

An example of this is with Direct Sequence Spread Spectrum Systems such as CDMA, a signal can be below the noise and still be detected.

## Is High SNR better than Low SNR?

In general, a high SNR is always better than low SNR. However there is a limit for every modulation scheme beyond which a higher SNR makes no difference to performance.

For instance, BPSK modulation requires an SNR of 7 dB for an error rate lower than 10-5. In this case improving the SNR to 10 dB will not provide any benefit if your BER requirement is the same.

## How to convert from SNR to volt?

SNR is a ratio expressed in decibel or dB. It is a relative quantity and as such does not have units. You can use this calculator to convert from dB to linear signal-to-noise voltage ratio.