Signal-to-Noise Ratio (SNR) Calculator

SNR is the ratio of desired signal power to unwanted noise power, usually expressed in decibels (dB). An SNR of 30.0000 dB means signal power is 1000.0000 times noise power — e.g. Ps = 10 mW and Pn = 0.01 mW. The larger the SNR, the cleaner the signal.

SNR(dB) = 10·log₁₀(Ps/Pn). Example: Ps = 10 mW and Pn = 0.01 mW gives SNR = 10·log₁₀(10/0.01) = 30.0000 dB. Enter power in W, mW, µW, nW, dBm, or dBW in the first tab — dBm/dBW units are auto-converted to watts first.

For rms voltage, SNR(dB) = 20·log₁₀(Vs/Vn). Example: Vs = 1 V and Vn = 1 mV gives SNR = 20·log₁₀(1000) = 60.0000 dB. Use the second tab if you measure with an oscilloscope or AC multimeter.

Because power is proportional to voltage squared (P = V²/R). 10·log(Ps/Pn) = 10·log((Vs/Vn)²) = 20·log(Vs/Vn) — the same formula, just different domains. Example: Vs/Vn = 1000 gives a power ratio of 1,000,000, and 10·log(1,000,000) = 60 dB = 20·log(1000).

Each stage adds noise figure (NF), so SNR_out = SNR_in − NF_total. NF_total is calculated with the Friis formula from each stage's NF and gain. Example: 40 dB input SNR through 3 stages (NF/gain: 3/10, 6/20, 8/15 dB) gives total NF 3.6148 dB, so output SNR = 36.3852 dB. The first stage contributes 86.80% — that's why

ENOB = (SNR_dB − 1.76) / 6.02. This formula inverts the ideal ADC relation (SNR = 6.02·N + 1.76 dB) so measured SNR — which includes real noise and distortion — translates to effective bits. Example: measured SNR 74 dB → ENOB = 12.0000 bits. A 12-bit ideal ADC itself is limited to 74.0000 dB SNR.

The Shannon–Hartley law: C = B·log₂(1 + SNR_linear), the theoretical limit of error-free data rate on an AWGN channel. Example: 20 MHz bandwidth with 20 dB SNR gives C = 20×log₂(101) = 133.1642 Mbps (spectral efficiency 6.6582 bit/s/Hz). Real systems are always below this number.

Invert the Shannon formula: SNR_linear = 2^(C/B) − 1. Example: for C = 100 Mbps at B = 10 MHz, required SNR = 30.0988 dB. In the high-SNR regime, each doubling of rate at fixed bandwidth demands about 3 dB more SNR.

Yes. Negative SNR means noise power exceeds signal power (e.g. Pn = 2 mW, Ps = 1 mW → SNR = −3.01 dB). Signals can still be decoded below the noise floor with spread-spectrum or strong coding techniques — GPS works at around −20 dB SNR. This calculator shows negative SNR as-is.

The Noise Figure Calculator (#1741 at nrtechstudio.com) answers “how much noise degradation a device/chain adds”: NF dB↔linear conversion, Friis cascade as total NF, and noise temperature Te. This SNR calculator answers “what is my signal-to-noise ratio”: from power/voltage, output SNR after cascade, ADC ENOB,

The Resistor Noise Calculator computes Johnson–Nyquist thermal noise of a specific resistor (Vn=√(4·kB·T·R·Δf), nV/√Hz density, kTB power) — component level. This SNR calculator works at system level: given signal power and noise power (from any source, including that resistor), it calculates SNR, ENOB, and capacity

Because RF/audio measurements are almost always reported in dBm (0 dBm = 1 mW). Example: a −20 dBm signal against a −80 dBm noise floor gives SNR = 60.0000 dB directly from the difference — the calculator converts both to watts then computes the ratio, with identical results.