Wi-Fi Signal: RSSI, Noise and SNR
The Wi-Fi bars hide three numbers that matter: signal, noise and the gap between them. This explains RSSI, SNR and dBm, what counts as good, and how to see yours live with Netutilus for Mac.
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free to download · macOS 14.6 or later
The Wi-Fi icon shows a few bars. Wi-Fi Analyzer shows the numbers behind them.
RSSI: signal strength
How strongly your Mac hears the router, in dBm. It’s always negative, and closer to zero is stronger:
- −50 dBm or higher: excellent. You’re near the router.
- −60: good.
- −70: fair. Speeds start to drop.
- Below −70: weak. Calls break up and the connection may drop.
Every 3 dB is half or double the power, so −70 is a hundredth of −50. Walls, floors and distance take it away fast.
Noise
The background hiss of the radio band: other electronics, distant networks. Usually around −90 to −100 dBm. It rarely changes much, but when it rises, everything gets harder to hear.
SNR: what actually matters
Signal-to-noise ratio is how far the signal stands above the noise: RSSI minus noise. A strong signal in a noisy place can be worse than a moderate one in a quiet place.
- 40 dB or more: excellent.
- 25 dB: good.
- 15 dB: fair.
- Below that: unreliable.
TX Rate
The speed the Mac and the router currently agree to talk at. It’s a ceiling, not what you get: real throughput is usually about half. It drops as the signal weakens.
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