Signal to Noise Ratio Calculator

How it is calculated

You enter signal power and noise power, both in the same unit (watts, milliwatts, any power unit, as only their ratio matters). The tool first divides: ratio = Psignal ÷ Pnoise. It then converts to decibels with SNR(dB) = 10 × log₁₀(ratio) and shows the result with two decimals, together with the plain ratio written as N : 1.

Both inputs must be greater than zero: zero noise would mean an infinite ratio, and zero or negative signal has no logarithm, so no result is shown. A ratio below 1 (more noise than signal) gives a negative dB value. The formula is for power. If your values are voltages or currents measured across the same resistance, square them first or use the factor 20 instead of 10.

Common mistakes

• Typing voltages or sound pressures into the power fields. The tool uses 10·log₁₀, so voltages give half the true dB; square them first, or double the result.
• Mixing units, for example signal in watts and noise in milliwatts. The ratio is then wrong by a factor of 1000, which is 30 dB.
• Entering the noise level in dB or dBm as if it were a power. Both fields need linear power values, not logarithmic ones; to use dB figures, simply subtract them instead.
• Entering 0 for noise to mean "no noise". A perfect, noise-free signal has an infinite ratio, and the tool gives no result for it.
• Swapping the two fields. Noise over signal gives the same number with the opposite sign, so a good link looks like −26.02 dB.