SNR Calculator
Calculate the signal-to-noise ratio from signal and noise power levels.
About SNR Calculator
Signal-to-noise ratio (SNR) is the difference, in dB, between the received signal power and the background noise floor: SNR(dB) = signal(dBm) − noise(dBm). Because both values are already logarithmic (dBm), the SNR calculation is a simple subtraction rather than a division. SNR is a better predictor of connection quality than signal strength alone, since a strong signal in a noisy environment can perform worse than a moderate signal in a quiet one — the modulation and coding scheme a radio can sustain depends directly on how far the signal sits above the noise.
Formula
Signal-to-noise ratio
SNR(dB) = signal(dBm) − noise(dBm)
- P_{signal}
- Received signal power in dBm
- P_{noise}
- Noise floor power in dBm
Worked example
With the default values below, SNR Calculator returns Signal-to-Noise Ratio of 35.0. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Signal Poweraccepts -100–0 dBm
- -55 dBm
- Noise Flooraccepts -110–-40 dBm
- -90 dBm
Results
- Signal-to-Noise Ratio
- 35.0 dB
- Quality Rating
- Good
- Expected Performance
- Reliable connection with good throughput; minor rate reduction possible.
Step by step
- 1Values used
- 2Signal-to-noise ratio
- 3Signal-to-Noise Ratio= 35.0 dB
- 4Quality Rating= Good
- 5Expected Performance= Reliable connection with good throughput; minor rate reduction possible.
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why is SNR a better indicator than raw signal strength?
A strong signal (e.g. -50 dBm) next to a high noise floor (e.g. -55 dBm) gives only 5 dB of SNR — poor quality — while a weaker signal (-70 dBm) with a very quiet noise floor (-95 dBm) gives 25 dB — good quality. Signal strength alone doesn't reveal this.
What SNR is needed for good WiFi performance?
Roughly 25 dB or higher is generally needed for a solid, high-throughput connection. Below about 15-20 dB, expect noticeably reduced data rates as the radio falls back to more robust but slower modulation schemes to maintain a usable link.
What causes a high noise floor?
Other wireless devices on the same or overlapping channels, non-WiFi interference (microwave ovens, Bluetooth, cordless phones), electrical equipment, and even thermal noise in the receiver itself all contribute to raising the effective noise floor.
Can SNR be negative?
Yes, if the noise floor exceeds the signal power (e.g. signal at -85 dBm with noise at -80 dBm gives -5 dB SNR), meaning the receiver essentially cannot distinguish the intended signal from background noise, and the link will fail.