SNR Calculator
Enter a signal and a noise amplitude to get the signal-to-noise ratio in decibels — and see why every 20 dB means a tenfold cleaner signal.
Amplitude form in decibels
Enter the signal and noise amplitudes in the same unit and the calculator returns the signal-to-noise ratio in decibels using 20·log10(signal/noise).
Use the same unit
Both amplitudes must be measured the same way — both peak or both RMS volts — so the ratio is meaningful. The unit cancels, so only the ratio matters.
What is the signal-to-noise ratio?
How clean a signal is
This SNR calculator turns two amplitude measurements — the signal and the background noise — into the signal-to-noise ratio in decibels. The signal-to-noise ratio describes how far a wanted signal stands above the noise floor, and it is one of the most important numbers in audio, radio, imaging, and communications: the larger it is, the cleaner and more usable the signal. When you measure amplitudes such as voltages, the ratio is expressed in decibels with the factor 20, because amplitude relates to power through a square. The calculator takes the signal amplitude and the noise amplitude in the same unit and returns the ratio in decibels.
Enter a signal amplitude and a noise amplitude in the same unit to get the signal-to-noise ratio in decibels instantly.
The signal-to-noise ratio in the amplitude form is twenty times the base-10 logarithm of the ratio of the signal amplitude to the noise amplitude.
SNR(dB) = 20 × log10(signal / noise)The signal and noise must be in the same unit, because only their ratio enters the formula — the unit cancels out. The factor 20 (rather than 10) is what makes this the amplitude form: amplitude is squared to get power, and squaring inside a logarithm doubles the multiplier. So an amplitude ratio of 10 becomes 20 dB.
Suppose you measure a signal amplitude of 2 V and a noise amplitude of 0.02 V.
Form the amplitude ratio
2 / 0.02 = 100 — the signal is a hundred times the noise amplitude.
Take the base-10 logarithm
log10(100) = 2 — the ratio expressed as a power of ten.
Multiply by twenty
20 × 2 = 40 dB — the signal-to-noise ratio in the amplitude form.
A higher decibel value means a cleaner signal: more wanted signal relative to the noise floor. The decibel scale is logarithmic, so the steps are multiplicative rather than additive. In the amplitude form, every extra 20 dB corresponds to a tenfold larger amplitude ratio: 0 dB means the signal and the noise are equal (a ratio of 1), 20 dB means the signal amplitude is ten times the noise, 40 dB means a hundred times, and 60 dB means a thousand times. A negative value means the noise is actually larger than the signal. As a rough guide, telephone-grade audio sits around 30 dB, good music recordings reach 60 dB or more, and high-end converters push well beyond 90 dB. Because the scale is logarithmic, a modest-sounding gain of a few decibels can represent a substantial real improvement in how clearly the signal cuts through the noise.
The formula is exact, but a couple of practical points decide whether your number is meaningful.
Amplitude form, power form, and consistent units
This calculator uses the amplitude (voltage) form, SNR = 20·log10(signal/noise), which is correct when you compare amplitudes such as voltages. If you instead start from powers, use the power form with the factor 10 — SNR = 10·log10(P_signal/P_noise) — because power is proportional to amplitude squared, and the two forms agree for the same physical ratio. Either way, both quantities must be in the same unit and measured the same way (both peak or both RMS), or the decibel value will be wrong.