Signal To Noise Ratio Calculator
The signal against the hiss — power ratio in and out of decibels, with a plain-language read on what the number means.
Signal To Noise Ratio Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Power ratios on matched impedance
- Broadband floor — no per-Hz density conversion
In short: One hundred milliwatts of signal against a tenth of a milliwatt of noise is a factor of exactly 1,000 — thirty decibels, speech-grade territory. Decibels compress ratios so that multiplication becomes addition: every ten of them is a factor of ten in power, every twenty a factor of ten in voltage. Below twenty dB the message drowns; above sixty the channel is cleaner than most measurement gear.
Formula
SNR(dB) = 10 × log₁₀(Ps ÷ Pn)
The decibel is a logarithm of a ratio: ten times the base-ten log of signal power over noise power. Ten dB is ten times the power, twenty is a hundred, thirty a thousand — each extra ten multiplies the ratio again. For voltage or current amplitudes on the same impedance the constant doubles to twenty per decade, which is why audio spec sheets seem to score differently from radio ones: same ratio, different ruler.
Worked Example
- Measure the power that carries the message.
- Measure the noise floor in the same units.
- Ten times log ten of the ratio is the answer.
Defaults: 100 mW against 0.1 mW — 30 dB, the thousand-to-one channel. Drop the noise to 0.01 mW and the grade climbs to 40 dB without touching the signal; halving the noise buys the same three dB wherever you start.
Strengths & Limits Of This Model
Where this engine is strong
- Both directions — ratio in, dB out, band explained
- Plain-language bands without fake standards
Where it stops
- No bandwidth or modulation gain in the grade
Practical Use Cases
Radio links
margin before the drop-out
Audio chains
hiss floor per stage
Instrument specs
reading datasheet dB honestly
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Signal To Noise Ratio Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why decibels instead of a plain ratio?
Real channels chain: cable, amplifier, receiver each multiply the ratio, and logs turn that multiplication into addition you can do in your head. Thirty dB of signal against three dB of noise floor is twenty-seven dB — no calculator required.
Ten log or twenty log?
Power ratios use ten; amplitude ratios use twenty, because power rides on the square of voltage. A twenty-volt-on-volt ratio and a forty-dB power ratio are the same channel expressed twice.
What SNR do I actually need?
Voice survives comfortably past twenty dB and struggles under fifteen; data links price their error rates on it directly; good audio wants fifty or better. The bands on this screen are plain-language guideposts, not standards.
How do I go from dB back to a ratio?
Divide by ten and raise ten to that power: thirty dB is ten cubed, a thousand. The ratio card on this screen does exactly that in reverse so the two forms stay honest together.
Does a bigger signal always win?
Only if the noise stays put. Raising the signal and the noise together — turning the volume up into a hiss — changes nothing. The ratio is what carries information, which is why the first move is usually to lower the floor, not raise the roof.
Where does noise come from?
Thermal agitation in every resistance, shot noise in currents, and the rest of the world coupling in. Below a few dB of physics floor no design improves it; above that, layout and shielding earn every decibel.
My spec sheet says dBFS — same thing?
No. dBFS is referenced to full digital scale, not to noise; it measures headroom, not clarity. Convert to a noise-referenced figure before comparing channels.
Noise power below my meter's floor?
Compute it from bandwidth and resistance instead: thermal noise is kTB, about four nanovolts per megahertz into fifty ohms squared. The meters stop where the physics starts.