Wi-Fi signal strength chart
This is the scale WiFi Heatmapper uses to color its heatmaps. The bands are a practical guide, not an official standard, but they match what most network engineers work with.
| Signal | Rating | What it means in practice |
|---|---|---|
| -50 dBm or better | Excellent | Fast and stable everywhere it reaches. Typical within a few meters of the access point. |
| -60 to -50 dBm | Good | Reliable for everything, including calls and HD streaming. |
| -67 to -60 dBm | Fair | Fine for browsing and streaming. -67 dBm is the common minimum for voice calls. |
| -75 to -67 dBm | Weak | Usable, but calls may stutter and speeds drop. |
| -85 to -75 dBm | Poor | Slow and drops out. Treat these spots as dead zones for practical use. |
| below -85 dBm | Unusable | Little or no usable connection. |
Two numbers are worth remembering. -67 dBm is the level Wi-Fi networks for voice and video calls are usually designed to: above it, calls stay smooth; below it, they start to stutter. -75 dBm is roughly where a connection becomes unreliable for everything, which is why spots below it are treated as dead zones.
What dBm means
dBm stands for decibels relative to one milliwatt. Wi-Fi signals arrive at your device with a tiny fraction of a milliwatt, so the values are negative: -40 dBm is a strong signal, -80 dBm a weak one. The number is often labelled RSSI (received signal strength indicator).
The scale is logarithmic. Every 3 dB halves or doubles the power, and every 10 dB is a factor of ten. So -70 dBm is not a little weaker than -60 dBm: it is a tenth of the power. That is why one extra wall or a few more meters can turn a good room into a poor one.
dBm, percent and bars
The bars on your phone or laptop are a rough summary of the same number, and every system draws them differently: a full icon can mean -45 dBm or -65 dBm. Windows often shows signal quality as a percentage instead. A common approximation is that 100% is about -50 dBm and every 2% is about 1 dB less, so 80% is roughly -60 dBm and 50% roughly -75 dBm. Drivers differ, so when you can get the value in dBm, use that.
Signal is not everything: noise
A strong signal helps only if it stands out from the background noise. The difference between the two is the signal-to-noise ratio (SNR). With a typical noise floor around -90 dBm, a signal of -65 dBm gives an SNR of 25 dB, which is comfortable. In busy places, such as apartment buildings with many networks, the noise and interference are higher, so the same signal strength can work worse. If the signal is good and Wi-Fi is still slow, interference or a crowded channel is the likely cause, not coverage.
How to check your Wi-Fi signal in dBm
| Device | How to see the value |
|---|---|
| Mac | Hold Option and click the Wi-Fi icon in the menu bar. The RSSI line is the signal in dBm. |
| Windows | Run netsh wlan show interfaces in Command Prompt. Use the Rssi line if it is there, otherwise the Signal percentage. |
| Linux | Run iw dev to find the interface name, then iw dev wlan0 link with that name. Use the signal value. |
| iPhone, iPad | Apple's free AirPort Utility, with its Wi-Fi Scanner turned on in Settings. |
| Android | A free app such as WiFiAnalyzer (open source) shows the connected network in dBm. |
Step-by-step instructions for phones are in measuring Wi-Fi signal on iPhone and Android.
One reading is not enough
The signal changes by a few dB from second to second, and a lot from room to room. A single number tells you how one spot was at one moment. To see where your coverage actually holds up, take readings in every room and look at them on the floor plan: that is a Wi-Fi heatmap.
WiFi Heatmapper does that for free in your browser: add a floor plan or sketch one, type the dBm value at each spot, and the map shows the strong and weak areas in the colors above. The full process is in how to make a WiFi heatmap.
