Signal-to-Noise Ratio Calculator finds SNR in dB from signal and noise power, voltage or dBm levels, or as a ratio from two values, a mean and deviation, or a USP HPLC peak height.
Power quantities use 10 × log₁₀. Enter the average signal power and noise power.
dB to Ratio Table
| SNR | Power | Voltage | Signal Share |
|---|---|---|---|
| 0 dB | 1:1 | 1:1 | 50% |
| 3 dB | 1.995:1 | 1.413:1 | 66.61% |
| 6 dB | 3.981:1 | 1.995:1 | 79.92% |
| 10 dB | 10:1 | 3.162:1 | 90.91% |
| 20 dB | 100:1 | 10:1 | 99.01% |
| 23.01 dB | 200:1 | 14.14:1 | 99.5% |
| 25 dB | 316.2:1 | 17.78:1 | 99.68% |
| 30 dB | 1,000:1 | 31.62:1 | 99.9% |
| 40 dB | 10,000:1 | 100:1 | 99.99% |
| 60 dB | 1,000,000:1 | 1,000:1 | Over 99.99% |
Signal vs Noise and Steps
- SNR (dB) = 10 × log₁₀(Ps ÷ Pn)
- Ps ÷ Pn = 0.2 W ÷ 0.001 W = 200
- SNR = 10 × log₁₀(200) = 23.01 dB
- Shannon limit = log₂(1 + 200) = 7.651 bit/s/Hz
Six SNR Types in the Signal-to-Noise Ratio Calculator
The Signal-to-Noise Ratio Calculator compares a wanted signal with the noise around it. Type of SNR picks the kind of numbers you have, and the fields change to match. Each type opens with a worked example already filled in.
| Type of SNR | What you enter | Loaded example | Result |
|---|---|---|---|
| Power SNR | Signal and noise power in W, mW or µW | 200 mW over 1 mW | 23.01 dB |
| Voltage SNR | RMS signal and noise voltage | 1 V over 10 mV | 40 dB |
| SNR from dB or dBm | Signal and noise level in dBm, dBW, dBV or dB | -65 dBm over -90 dBm | 25 dB |
| Simple ratio | Any two values in one unit | 80 over 20 | 4:1 |
| Mean and standard deviation | Mean and standard deviation, or a list of raw readings | 50 over 2.55 | 19.61:1 |
| HPLC peak | Peak height H, noise range h and sample concentration | 25 over 4 | 12.5:1 |
The first three types answer in decibels and add the plain ratio beside it. The last three answer as a ratio and add the dB reading. A Target SNR or Target Ratio field then shows what signal or noise level would get you there.
Each group has one extra field. The dB types take a channel bandwidth for the data rate row. The mean type takes a list of readings, and the HPLC type takes the concentration you injected.
Signal-to-Noise Ratio Formula in dB
How do you calculate the signal-to-noise ratio? Divide the signal by the noise, then take a logarithm if you want decibels. The multiplier in front of the logarithm depends on whether the two values are powers or voltages.
$$SNR_{dB} = 10 \times \log_{10}\left(\frac{P_s}{P_n}\right)$$
P_s and P_n are the average signal and noise power in the same unit. For the example loaded in the Signal-to-Noise Ratio Calculator, 200 mW over 1 mW is a ratio of 200, and 10 times its logarithm is 23.01 dB.
$$SNR_{dB} = 20 \times \log_{10}\left(\frac{V_s}{V_n}\right)$$
V_s and V_n are RMS voltages measured across the same impedance. Power goes with voltage squared, and squaring inside a logarithm doubles the multiplier. So 1 V over 10 mV is a voltage ratio of 100 and a power ratio of 10,000, and both read 40 dB.
When both levels are already in decibels, the signal-to-noise ratio formula in dB is a subtraction. Cisco Meraki’s Wi-Fi guide gives a client at -75 dBm over a noise floor of -90 dBm, which is 15 dB.
$$SNR_{dB} = S_{dB} – N_{dB}$$
Both levels must sit on the same scale. You pick dBm, dBW, dBV or plain dB on the signal row, and the noise row follows it, so the two cannot be mixed. The same subtraction works on the output of an EIRP Calculator link budget, once path loss gives you the received level in dBm.
The Signal-to-Noise Ratio Calculator also works as an SNR to dB calculator in reverse. The dB to Ratio Table lists the power ratio, voltage ratio and signal share for common dB values, and marks your own row.
| SNR | Power ratio | Voltage ratio | Signal share of total power |
|---|---|---|---|
| 0 dB | 1:1 | 1:1 | 50% |
| 3 dB | 1.995:1 | 1.413:1 | 66.61% |
| 6 dB | 3.981:1 | 1.995:1 | 79.92% |
| 10 dB | 10:1 | 3.162:1 | 90.91% |
| 20 dB | 100:1 | 10:1 | 99.01% |
| 30 dB | 1,000:1 | 31.62:1 | 99.9% |
| 40 dB | 10,000:1 | 100:1 | 99.99% |
For a signal to noise ratio calculator in Excel, put the signal in B1 and the noise in B2. Power values use =10*LOG10(B1/B2) and voltages use =20*LOG10(B1/B2). A column of readings uses =AVERAGE(A2:A21)/STDEV.S(A2:A21).
What 80% Signal and 20% Noise Means
An 80% signal and 20% noise mix is a ratio of 80 over 20, or 4:1. The Simple Ratio type of the Signal-to-Noise Ratio Calculator loads with exactly that. It reads 6.02 dB if the two values are powers and 12.04 dB if they are voltages or amplitudes.
A bare ratio has no single dB value, which is why the tool shows both. The result note says so and points you to Power SNR or Voltage SNR when you know which quantity you measured.
The 80/20 phrase mostly comes from signal-to-noise ratio in business talk. Investor Kevin O’Leary told the Diary of a CEO podcast that Steve Jobs worked at “80 signal, 20 noise”, as Fortune reported. He said Elon Musk “has no noise” across the 18 hours he is awake.
In that use, signal is the few tasks that matter today and noise is everything else. It is a figure of speech, not a measurement, but the arithmetic is the same 4:1.
What Is a Good Signal-to-Noise Ratio?
A good value depends on the job, so one number does not fit every field. Is a high SNR good or bad? Higher is always better for the signal. Above 0 dB the signal is stronger than the noise, at 0 dB they are equal, and a negative figure means noise is on top.
| Use | Mark | Source |
|---|---|---|
| Wi-Fi data network | 20 dB or more | Cisco Meraki |
| Wi-Fi voice applications | 25 dB or more | Cisco Meraki |
| Detection limit in an assay | 3:1, or 2:1 | ICH Q2(R1) |
| Quantitation limit in an assay | 10:1 | ICH Q2(R1) |
| Gen 3 night vision tube, commercial grade | 25 minimum | Steele Industries |
| Gen 3 night vision tube, mil-spec grade | 28 minimum | Steele Industries |
| Ideal 16-bit converter | 98.08 dB | Analog Devices MT-001 |
For a good Wi-Fi signal-to-noise ratio, enter both levels in dBm and the Signal-to-Noise Ratio Calculator rates the result against the two Meraki marks. The loaded -65 dBm over -90 dBm clears both at 25 dB. Meraki’s own 15 dB example sits 5 dB under the data mark, and Meraki notes that signals near the noise floor get corrupted and resent.
Power, voltage and the other dB scales get no pass mark, because the right figure depends on the system. Their second card shows what the noise does to a meter reading instead. At 23.01 dB the noise is 0.5% of the signal power and lifts the reading by 0.02166 dB. Keeping that error under 0.1 dB against 1 mW of noise takes a 42.93 mW signal, which is 16.33 dB.
A good signal-to-noise ratio for night vision is quoted as a plain number, not in dB. Steele Industries lists modern Gen 3 tubes from 18 to 36 and above. A tube’s figure of merit is its SNR multiplied by its center resolution in lp/mm.
A car amplifier spec sheet quotes its signal-to-noise ratio in dB. A spec of 80 dB means the rated output voltage is 10,000 times the noise voltage, and 100 dB means 100,000 times. Enter the two voltages in Voltage SNR to check a figure, or read the ratio off the dB to Ratio Table.
HPLC Signal-to-Noise by USP 2H/h
To find signal-to-noise ratio in HPLC, measure the peak height H from the peak top down to the baseline. Then measure h, the full range of the baseline noise from its highest to its lowest point. USP and EP both give the same formula.
$$S/N = \frac{2H}{h}$$
The 2 is there because the noise is counted as half its peak-to-peak range. A peak 25 units high over a 4 unit noise range gives 12.5:1. The first card also shows the plain H/h of 6.25:1 and half the noise range, so you can match either convention.
Where you read h changes the answer. Waters’ note on the USP method gives the window as at least 5 times the peak width at half height, centered on the peak where possible. Shimadzu’s pharmacopoeia summary notes that USP went back to that window from 20 times in 2023, while the Japanese Pharmacopoeia still uses 20 times.
The rule of 3 in HPLC is the limit of detection. ICH Q2(R1) accepts a signal-to-noise ratio of 3:1, or 2:1, for the detection limit and calls 10:1 typical for the quantitation limit. At 12.5:1 the example peak clears both marks.
The limit of detection (LOD) in HPLC is usually wanted as a concentration. The HPLC type of the Signal-to-Noise Ratio Calculator scales the concentration you injected down to the 3:1 and 10:1 marks.
$$LOD = \frac{3 \times C}{S/N}$$
C is the sample concentration and S/N is the measured ratio. A 0.5 µg/mL sample at 12.5:1 gives an estimated LOD of 0.12 µg/mL and, with 10 in place of 3, an LOQ of 0.4 µg/mL. Both assume the detector response is linear down through zero.
The same two marks carry over to signal-to-noise ratio in spectroscopy and other lab readings. The Mean and Std Dev type applies them to repeated readings, where the ratio is the mean over the standard deviation.
$$SNR = \frac{\mu}{\sigma}$$
You can type the two values or paste the raw readings. The loaded list is 48, 52, 50, 47 and 53. Its mean is 50 and its sample standard deviation, with n – 1 in the divisor, is 2.55. Typing a mean or deviation by hand clears the list.
That makes the ratio 19.61:1, or 25.85 dB as an amplitude ratio. The coefficient of variation is the same ratio turned over, 5.1%. The power form squares both values and gives about 385.
How to Improve Signal-to-Noise Ratio
There are only two levers, more signal or less noise. The target card in the Signal-to-Noise Ratio Calculator prices both. To lift the 23.01 dB example to 35 dB, the signal must rise by 11.99 dB to 3,162 mW, or the noise must fall to 0.06325 mW.
When the noise is random, averaging repeated runs is the cheapest way to get a better signal-to-noise ratio. Noise amplitude falls with the square root of the run count. The Signal Averaging Table works it out from your own ratio, shown here for the 4:1 example.
| Runs averaged | Ratio | As 20 log dB | Hits 10:1 |
|---|---|---|---|
| 1 | 4:1 | 12.04 dB | No |
| 4 | 8:1 | 18.06 dB | No |
| 9 | 12:1 | 21.58 dB | Yes |
| 16 | 16:1 | 24.08 dB | Yes |
| 25 | 20:1 | 26.02 dB | Yes |
| 100 | 40:1 | 32.04 dB | Yes |
Going from 4:1 to 10:1 needs a gain of 2.5, and 2.5 squared is 6.25, so the card rounds up to 7 runs. The cost climbs fast. Doubling the ratio takes four times the runs, and ten times the ratio takes a hundred.
That square-root rule is how to increase signal-to-noise ratio in MRI as well. Radiopaedia gives SNR as proportional to voxel volume and to the square root of the number of averages. A narrower receiver bandwidth and surface coils cut the noise side.
An SNR calculator for astrophotography follows the same rule when frames are stacked, so 16 frames give four times the ratio of one. A single frame needs a camera noise model with shot noise, read noise and dark current, which the Signal-to-Noise Ratio Calculator does not include.
Shannon Limit and ADC Bits
The dB types finish with what the ratio can carry. Shannon’s limit is the base-2 logarithm of 1 plus the power ratio, in bits per second for each hertz of bandwidth. At 200:1 that is 7.651 bit/s/Hz. The Channel Bandwidth field turns it into a rate, 153 Mbit/s for the loaded 20 MHz channel, and accepts anything from hertz to gigahertz.
Converters tie bits to SNR the other way. Walt Kester’s MT-001 tutorial for Analog Devices gives an ideal N-bit converter an SNR of 6.02N + 1.76 dB for a full-scale sine wave. The 23.01 dB example equals 3.53 ideal bits.
Reading the Signal-to-Noise Ratio Calculator Result
What does an SNR of 5 mean?
It depends on the unit. A ratio of 5:1 means the signal is five times the noise, which is 6.99 dB for powers and 13.98 dB for voltages. An SNR of 5 dB is weaker, a power ratio of 3.162:1. In an assay, 5:1 is detectable but under the 10:1 quantitation mark.
What is the purpose of SNR?
It tells you how far a measurement can be trusted. Signal-to-noise ratio theory treats every reading as a wanted part plus a random part. The ratio between them sets how small a change you can detect, how much data a channel can carry, and how clean audio or an image looks.
How do I read the Signal Share row?
Signal Share of Total Power is the signal power over signal plus noise. At 0 dB it is 50%, at 10 dB it is 90.91% and at 20 dB it is 99.01%. The Signal-to-Noise Ratio Calculator draws it as a bar in the Signal vs Noise and Steps panel.
Why do power and voltage give the same dB?
They describe one signal two ways, so the dB figure has to agree. A voltage ratio of 10:1 is a power ratio of 100:1 across the same impedance, and both are 20 dB. More energy and power tools sit in the Energy, Work and Power Calculators hub.