Signal-to-Noise Ratio (SNR)
SNR in dB from signal and noise levels in dB, or from two values: 10 log10 for power, 20 log10 for voltage or amplitude. Shows power and amplitude ratios. How it works
Use the Signal-to-Noise Ratio (SNR)
About the Signal-to-Noise Ratio (SNR)
A signal 10 times the noise is an SNR of 10 dB if the values are powers and 20 dB if they are voltages or other amplitudes: SNR = 10 log10(Ps ÷ Pn) for power and 20 log10(Vs ÷ Vn) for amplitude. This SNR calculator works from two levels in dB or from two values, and shows the power ratio and the amplitude ratio for every result.
Signal-to-noise ratio in dB: power vs amplitude
| Signal ÷ noise | SNR if power (10 log10) | SNR if voltage or amplitude (20 log10) |
|---|---|---|
| 0.5 | -3.01 dB | -6.02 dB |
| 1 | 0 dB | 0 dB |
| 2 | 3.01 dB | 6.02 dB |
| 10 | 10 dB | 20 dB |
| 50 | 16.99 dB | 33.98 dB |
| 100 | 20 dB | 40 dB |
| 1,000 | 30 dB | 60 dB |
| 10,000 | 40 dB | 80 dB |
| 1,000,000 | 60 dB | 120 dB |
dB to power ratio and amplitude ratio
| SNR (dB) | Power ratio | Amplitude ratio |
|---|---|---|
| -3 | 0.501187 | 0.707946 |
| 0 | 1 | 1 |
| 3 | 1.99526 | 1.41254 |
| 6 | 3.98107 | 1.99526 |
| 10 | 10 | 3.16228 |
| 20 | 100 | 10 |
| 30 | 1,000 | 31.6228 |
| 40 | 10,000 | 100 |
| 60 | 1,000,000 | 1,000 |
| 80 | 100,000,000 | 10,000 |
| 120 | 1,000,000,000,000 | 1,000,000 |
Frequently asked questions
- When do I use 10 log or 20 log for SNR?
- Use 10 log10 for power quantities such as watts, and 20 log10 for amplitude quantities such as volts, amps or sound pressure, because power goes with amplitude squared. A voltage ratio of 50 is 33.98 dB, the same as a power ratio of 2,500.
- How do I calculate SNR from two dB levels?
- Subtract the noise level from the signal level, with both on the same reference (dBm with dBm, dBV with dBV). A signal at −10 dB over noise at −90 dB is 80 dB, a power ratio of 100,000,000.
- Can SNR be negative?
- Yes, when the noise is stronger than the signal. A signal at −95 dB with noise at −90 dB is −5 dB, a power ratio of 0.316228.
- What is 3 dB or 6 dB as a ratio?
- 3 dB is a power ratio of 1.99526, close to 2, and an amplitude ratio of 1.41254. 6 dB is a power ratio of 3.98107 and an amplitude ratio of 1.99526.
- Does the impedance matter for a voltage SNR?
- Not when signal and noise are measured across the same impedance: it cancels in the ratio, so the calculator does not ask for it.
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