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Wi-Fi Signal Strength Explained: That -70 dBm RSSI Value and How It Matters

You walk around the house and, at times, can see the Wi-Fi signal strength bars on your device move up or down. If you ever wonder what changes when you lose a bar or gain one, this post is for you.

You’ll learn about dBm and how it’s used to gauge Wi-Fi signal strength. In most cases, this is for your information only. There’s not much you can do about the signals other than moving your device or the Wi-Fi broadcaster around.

However, in some cases, knowing how to adjust the dBm-based triggers in a mesh system can help with roaming or signal hand-off. The whole thing can be a bit confusing until you’re through with this post.

Dong’s note: I initially posted this as part of the piece on Asus’s AiMesh and moved it out to a separate post on August 22, 2021, to add more information and clarify the subject matter.

Wi-Fi 6E Routers
All routers have one thing in common: We can’t see their signals. Or can we?

Wi-Fi Signal Strength and dBm

Wi-Fi signal strength is measure in dBm, short for decibels relative to a milliwatt.

dBm explained

There are two things you should remember about dBm:

  • It’s used in negative values: The lower the number, the higher the value, the stronger the signal. So -30 dBm is stronger than -60 dBm.
  • dBm doesn’t scale like most measurements (weight, length, etc.) — it’s not linear and consistently incremental. Instead, it’s logarithmic and spiral — it’s curvy. As a result, the gap between -30 dBm and -60 dBm might not be more significant than between -60 dBm and -65 dBm.

By the way, in case you wonder why the value is always negative: That’s because, due to the sensitive nature of the wireless signals, the value is always below one milliwatt.

Generally, meaningful dBm values range from -10 (strongest) to -90 (weakest). Here are the general dBm readouts:

  • Below -30 dBm: Too good to be true, or signal saturation (not good).
  • -30 dBm: The best possible.
  • -50 dBm: Excellent signals.
  • -60 dBm: Very good signals.
  • -65 dBm: Good, reliable signals. Up to now, you’ve always had full bars.
  • -70 dBm: This is the threshold where you might have lost a signal bar and are about to lose another, if not already. But the connection is still solid.
  • -75 dBm: This is where things start getting problematic, but the connection might still be useable.
  • -80 dBm: Borderline useless — you barely have just one bar.
  • -90 dBm: The signal is really weak, (almost) impossible to connect to.

Again, the significance of the numbers above varies slightly depending on the environment and hardware. Like all things in Wi-Fi, these are not hard values — expect nuances.

How to find out the dBm of your current received Wi-Fi signal strength

When a Wi-Fi device connects to a broadcaster, it’s connected at a certain dBm value which constantly changes in real-time, depending on the environment and the distance.

Wi Fi Analyzer
A Wi-Fi analyzer app will give you the signal strength of each broadcaster to a device in real-time.

Depending on the application, this value is called differently, but the most popular name is the received signal strength indicator or RSSI.

The easiest way to know a device’s received Wi-Fi signal strength is to use a Wi-Fi analyzer or Wi-Fi finder app.

Run the app, and it can visualize for you what dBm values your current devices have, both on the broadcaster and receiver’s sides, as you can see in the screenshot above.

If you’re on a Mac, there’s another easy way to figure out the machine’s current received Wi-Fi signal strength:

Click on the Wi-Fi icon while holding down the Option key. Now you’ll see the Wi-Fi signal strength shown as the RSSI value.

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Wi-Fi Signal Strength and other Information on a Mac
Option + click on the Wi-Fi icon will bring up lots of information about your Wi-Fi connection on a Mac. Note the RSSI value.

When you can (and should) change the dBm value

Generally, you can’t manually change the dBm value. That’s because it’s what your Wi-Fi client gets at a certain distance from the broadcaster. It is what it is. To change it, you have to move your device around physically.

However, when you use multiple broadcasters, i.e., a mesh Wi-Fi system, changing the dBm value might help devices roam seamlessly.

In this case, you actually change the dBm values of the triggers. In other words, you don’t change the value but only what will happen when the value gets to a certain number.

Specifically, when you have multiple broadcasters in a home and want your Wi-Fi device in your hand, like a phone, to automatically connect to the nearest broadcaster instead of the one farther away, adjusting the dBm triggers on the broadcasters might help.

By the way, this is generally called seamless handoff, which is always a tricky business.

Picking the right dBm value

Not all mesh systems allow you to change the dBm triggers — most only allow you to turn the seamless handoff on or off.

One of the systems I know that gives you this option is Asus’s AiMesh, and I’ll use it as an example.

Roaming Assistant setting within an Asuss AiMesh router and the default Wi-Fi Signal Strength in dBm
Here’s the Roaming assistant setting within an Asus AiMesh router’s web interface. Note the default received Wi-Fi signal strength (RSSI) which is -70 dBm.

In this case, you can adjust the dBm value of the Roaming assistant setting for each frequency band (2.4GHz, 5GHz, or 6GHz). And even then, it’s a bit finicky.

That’s because, depending on the environment, a router picks a dBm value that works best with the seamless handoff.

Consequently, you might find this number different from one router to another or one location to another. However, you can use the default value as the base.

Speaking of default, the number you’ll likely see is -70 dBm, the “sweet spot” threshold where the signal is still around 60%.

At this level, a client would disconnect itself from the current node when the signal strength gets around 2 bars, and it detects another node with a stronger signal nearby. It then connects itself to the closer node.

So, if you want the hand-off to take place at a higher threshold (like 3 bars), increase the dBm value a few points from the base (-67 dBm or so). Now, your phone won’t wait till the signal gets as low as two bars before it jumps.

If you change it to an even higher value (like -60 dBm), the hand-off might happen too frequently, which can be a bad thing, especially when you stay right in the middle of two nodes.

That’s because each jump takes a bit of time for the client to re-authenticate with the new node. Hence, too many jumps close to one another can cause interruption.

On the other hand, if you change the value to lower than -70, the hand-off might not happen at all, and your phone remains connected to a node until there’s no signal from it.

But, generally, I’d keep the value of dBm between -60 (less clingy, faster speed) and -75 (more clingy, slower performance).

The takeaway

Again, most of the time, knowing the current dBm on your device is just for your information. Maybe so that you can adjust your device’s or your Wi-Fi broadcaster’s position.

In a few cases, changing the dBm-based trigger can help with roaming in a mesh setup. But even then, keep in mind that Wi-Fi can be unpredictable and doesn’t always work as to how we perceive the physical world.

That’s because, with Wi-Fi, we literally get what we don’t see. So don’t expect it to behave the way you see things. Most of the time, this is a matter of trial and error.

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7 thoughts on “Wi-Fi Signal Strength Explained: That -70 dBm RSSI Value and How It Matters”

  1. Great article Dong.

    Question 1:
    I understand from your article, you are showing/using Asus RT-AX89X router but not sure what other satellite hub(s) that you are using to form the mesh system. Or are you using another Asus AP/router to form AIMesh?

    Question 2:
    Generally, how long does it takes to switch from one router (hub) to another hub in a mesh using traditional routers like Asus RT-AX89X? Will the zoom video call be interrupted during the switch over?

    Question 3:
    Will the switching process be faster or user experiences be better if one uses mesh specific routers like Asus ZenWiFi or Netgear Orbi?

    Reply

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