Short answer: Wi-Fi signal strength is measured in dBm, a negative number where closer to zero is stronger: −50 dBm is a strong signal, −80 dBm is a weak one. Windows shows it as a percentage, a Mac shows the dBm figure in its Wi-Fi details, and most router apps show it for every connected device. As a working rule, aim for about −70 dBm or better where you use Wi-Fi most.
On Windows
Open Command Prompt and run netsh wlan show interfaces. Microsoft documents this command as listing your wireless interfaces and their connection details, and the Signal line shows the strength of the current connection as a percentage.
The percentage maps onto dBm. Microsoft’s documentation for the Windows Wi-Fi interface says a signal quality of 0% corresponds to −100 dBm and 100% to −50 dBm, with values in between on a straight line. So:
| Windows Signal | Approximate dBm |
|---|---|
| 100% | −50 or stronger |
| 80% | −60 |
| 60% | −70 |
| 40% | −80 |
| 20% | −90 |
A reading of 100% only tells you the signal is at least −50 dBm; anything stronger also shows as 100%.
On a Mac
Hold the Option key, click the Wi-Fi icon in the menu bar and choose Open Wireless Diagnostics. Its Performance window graphs the signal (shown as RSSI, in dBm) and the background noise over time, so you can carry a laptop from room to room and watch the number change.
On phones, and in your router’s app
Phones show signal as bars rather than numbers. For a figure, the router’s app is usually the easiest place to look, because it shows every device at once.
ASUS is a good example: its router app and admin page list each connected device with its band and its signal in dBm. ASUS classes −20 to −70 dBm as good, −71 to −80 dBm as fair, and −81 dBm or lower as weak. Other brands’ apps show the same information as bars or labels. Walk around with your phone and watch its entry in the app update.
What the numbers mean
There’s no single official scale, but the vendors that publish thresholds broadly agree:
| Signal | What it means |
|---|---|
| −50 dBm or better | Strong; you’re close to the router or access point |
| −50 to −70 dBm | Normal working signal for most uses |
| −70 to −80 dBm | Marginal; works for browsing, but speed drops and some devices start looking elsewhere |
| Below −80 dBm | Poor; expect slow speeds and drops |
Juniper Mist, which makes enterprise Wi-Fi systems, calls anything below −80 dBm poor, treats −70 to −80 dBm as dependent on the device, and describes −50 to −70 dBm as the typical range devices work in. ASUS draws its good/fair line at −70 dBm.
Apple’s own devices show where “marginal” starts in practice. Apple says an iPhone or iPad holds on to its current access point until the signal falls past −70 dBm, and a Mac until −75 dBm, and only then looks for a better one. On a mesh network, that’s why a phone can cling to a far node: until it crosses its threshold, it doesn’t look.
How to use it to place hardware
- Pick three or four spots where you actually use Wi-Fi, including the worst one.
- Take a reading in each with the same device, standing in the same place. Note the band (2.4, 5 or 6 GHz); Wi-Fi bands explains why they differ.
- Make one change, such as moving the router or adding a node, and measure the same spots again.
- Aim for about −70 dBm or better where it matters. Weaker than that, and the next step is the dead zone checks or better router placement.
The same readings help with extra hardware. An extender or mesh node needs a good signal from the router where you put it, not at the edge of coverage: where to put an extender and how many mesh nodes you need both start from that.