Enter your signal power and noise power (or amplitude values) to calculate the Signal-to-Noise Ratio (SNR) in decibels and as a simple ratio. Choose your SNR type — Power SNR, Voltage/Amplitude SNR, or dB subtraction — and the calculator returns the SNR in dB along with the linear SNR ratio and a quality assessment of your signal.
SNR (in dB)
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Linear SNR Ratio
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Signal Quality
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Signal as % of Total
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Noise as % of Total
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SNR is a measure of the strength of a desired signal relative to the background noise. A higher SNR means the signal is clearer and less corrupted by noise. It is commonly expressed in decibels (dB) and is used in audio, wireless communication, imaging, and many other engineering fields.
Generally, an SNR above 40 dB is considered excellent, 20–40 dB is good, 10–20 dB is acceptable, and below 10 dB is poor. For Wi-Fi connections, 25 dB or higher is recommended for reliable performance. The required SNR depends heavily on the application — voice calls need less than high-definition data transmission.
For power-based measurements, use SNR(dB) = 10 × log₁₀(P_signal / P_noise). For voltage or amplitude measurements, use SNR(dB) = 20 × log₁₀(V_signal / V_noise). If both signal and noise are already in dB, simply subtract: SNR = Signal(dB) − Noise(dB).
Power SNR uses a factor of 10 in front of the logarithm (10·log₁₀), while Voltage or Amplitude SNR uses a factor of 20 (20·log₁₀). The factor doubles because power is proportional to the square of voltage (P ∝ V²), so squaring inside the log pulls the exponent out as a multiplier of 2.
When both signal and noise values are already expressed in dB, you simply subtract them: SNR = 450 dB − 350 dB = 100 dB. This is an extremely high SNR, indicating an almost perfectly clean signal with negligible noise.
Common noise sources include thermal noise (Johnson–Nyquist noise) caused by heat, shot noise from random electron movement, flicker (1/f) noise in electronic components, electromagnetic interference (EMI) from nearby devices, and quantization noise in digital systems. Each type can degrade SNR differently depending on the application.
SNR directly limits how much information can be reliably transmitted over a channel — a concept formalized by Claude Shannon's channel capacity theorem. A higher SNR allows faster data rates with fewer errors. Low SNR forces systems to use slower speeds, stronger error correction, or results in dropped connections.
Yes, SNR can be negative in dB, which means the noise level is actually higher than the signal level. This occurs when P_noise > P_signal (or V_noise > V_signal). A negative SNR indicates that the signal is buried in noise and is very difficult to extract reliably without advanced signal processing techniques.