How to check Wi-Fi signal strength on iPhone, in dBm
The three Wi-Fi bars on an iPhone are a rough summary. Apple's own free app can show the real signal level in dBm, and once you can read it, finding the weak spots at home becomes easy.
In short
- Install Apple's free AirPort Utility, turn on Wi-Fi Scanner in the iPhone's Settings, then use Wi-Fi Scan in the app. Your network appears with its RSSI in dBm.
- Closer to zero is better: -50 dBm is excellent, -67 dBm is the level professionals use as the minimum for calls and video, -80 dBm is unreliable.
- An iPhone starts looking for a better access point only when the signal drops below -70 dBm, according to Apple's own documentation.
- Other App Store apps can't read this value on an iPhone. They show speed or response time instead, which answers a different question.
On this page
On an iPhone the Wi-Fi icon has three bars, and that's all iOS shows you. It doesn't publish how strong the signal has to be for each bar, and two bars can hide very different situations. If you're trying to work out why the bedroom is slow or where to put a mesh node, you need the number underneath: the signal level in dBm.
There's exactly one way to see it on an iPhone, and it's free and made by Apple.
Turn on the Wi-Fi scanner in AirPort Utility
AirPort Utility was made to configure Apple's AirPort routers, which Apple no longer sells. It's still on the App Store, and it contains a Wi-Fi scanner that works with any router.
- Install AirPort Utility from the App Store. It's free and published by Apple.
- Open the iPhone's Settings app, scroll down to the list of apps and tap AirPort Utility.
- Turn on Wi-Fi Scanner.
- Open AirPort Utility. In the top right corner tap Wi-Fi Scan, then Scan.
The app lists every network it can hear, yours and your neighbours'. For each one you'll see the network name, its RSSI in dBm, the channel and when it was last seen. The scan runs for a while and refreshes the values; tap Stop to end it.
If your router has several access points, or a mesh system, the same network name can appear more than once, one line per unit and band. The line with the strongest RSSI is usually the one your iPhone is connected to.
What the numbers mean
RSSI is always negative. The closer to zero, the stronger the signal. Because the scale is logarithmic, small differences matter: a drop of 3 dB halves the signal, a drop of 10 dB leaves a tenth.
- -30 to -50 dBm: excellent. You're in the same room as the router, or close to it.
- -50 to -67 dBm: good. -67 dBm is the level Cisco uses as the minimum when designing networks for calls and video.
- -67 to -75 dBm: usable for browsing and messages; video calls and streaming begin to suffer, and uploads first.
- -75 to -85 dBm: weak. Pages hang, video stalls, devices drop off.
- Below -85 dBm: the connection is barely there.
One more number is worth knowing. Apple documents that an iPhone keeps its current access point until the signal falls below -70 dBm, and only then looks for a better one. That's why, in a home with a mesh system, a phone can stay on a distant unit with mediocre signal instead of switching to the one next to you. Phone won't switch to the nearest node explains what to do about it.
Use it to map your home in ten minutes
The scanner becomes really useful when you walk with it.
Start next to the router and note the value. Then walk to each room you care about and take a reading where you actually use it: the desk, the bed, the sofa. Hold the phone the same way each time and wait a few seconds for the value to settle, because it moves by a few dB from one moment to the next.
What you're looking for is the shape of the change. A value that falls a little in every room means distance. A value that falls by 15 dB or more as you step through one door means that wall or that room is the obstacle. What blocks Wi-Fi at home explains how to read those drops.
The channel column tells you the band as well. Channels 1 to 13 are 2.4 GHz; channels from 36 upward are 5 GHz. If your router uses one name for both bands, you'll see both lines, and you can compare how each band holds up in the far rooms.
What the scanner doesn't tell you
The signal level measures how strongly the router reaches your iPhone. It doesn't tell you how well the router hears your iPhone in return, which matters for uploads and calls. It doesn't measure your internet speed, and it doesn't show interference directly, although the list of neighbouring networks on the same channel is a good hint.
That's why a room can show a decent -62 dBm and still feel slow. When the signal is fine and the connection isn't, the cause is somewhere else: see full bars but slow Wi-Fi.
Other ways to see the signal
On a Mac, hold the Option key and click the Wi-Fi icon in the menu bar: RSSI and noise appear directly, in dBm.
On Android, the network details in Settings show the signal as a word and often the link speed; Wi-Fi analyser apps show the exact dBm.
In your router or mesh app, the list of connected devices often shows each device's signal or connection speed, which is useful for a TV or a console.
Third-party App Store apps can't read the signal level on an iPhone: iOS doesn't give it to them. That's why the iPhone apps that test Wi-Fi, ours included, measure something else, such as speed or how quickly and steadily the router responds. Both views are useful, but they answer different questions, and only AirPort Utility gives you the dBm on an iPhone.