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*Log _{10}(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 Code Division Multiple Access (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.

**How to measure SNR?**

One method to measure SNR voltages is to use an oscilloscope shown in the picture below.

**The first step is to measure the RMS value of the signal and noise**

Modern oscilloscopes like the one above have built-in Math functions to do this. It essentially performs this RMS computation.

Let’s call this **V _{S+N}**

**The next step is to measure the RMS voltage of the signal alone**

In the video below, Mark Schnittker shows how to measure the signal voltage in a very noisy signal. Here are the steps:

- Input the signal to be measured to Channel 1 of the scope
- Input the clean reference signal to Channel 2 of the scope and trigger using this signal
- Average the noise on Channel 1 (using 128 averages in this case)
- You should now be able to see the sine wave that has a fixed phase relationship with the signal on channel 2
- Measure the root-mean-square (RMS) voltage value

Let’s call this value **V _{S}**

**The final step is to do the math**

The RMS noise voltage is **V _{N}** =

**V**–

_{S+N}**V**

_{S}The SNR is then given by **V _{S}**/

**V**_{N}This is a linear value and can be converted to the dB equivalent using the calculator on this page.