So following on from my basic WiFi setup recommendations thread from yesterday, how do you actually know if your WiFi connection is good or not?

It all comes down to signal strength in the end... (thread)

(Oops, life gets in the way sometimes)

You can use the little signal strength meter thingo on your device, but those are usually calibrated to show if your connection is “ok”, “poor” or “terrible”.

To really know how good your connection is, you need a number...

Signal strength of WiFi networks is measured in dBm - decibels of milliwatts. If you know about dB scales, you know I’m about to talk about either very large or very small numbers, and if you know about milliwatts, you know I’m about to talk about small amounts of power

Put two and two together, and I’m about to talk about very small amounts of power.

Your microwave oven puts out about 1000W in the 2.4GHz ISM band, but most of that is contained within what is effectively a faraday cage. 0dBm is 1mW, which is 1/1000 of 1W.

Typical power of WiFi equipment is usually +20dBm - 100mW, or 1/10,000 of the power of your microwave oven.

The transmission power that your device eventually receives drops off the further away from the transmitter you are, and drops quickly when objects are in the way

My usual recommendation for receive power is better than -65dBm for areas in your home you want good throughput (eg for video streaming), and better than -75dBm everywhere you want basic connectivity.

To put this in perspective, -70dBm is 0.0000000001W

The question now is, how do you know what the actual receive power of your device is? Apple iOS devices are great for this (surprisingly). All you need is the Apple AirPort utility, even if you don’t have an Apple AirPort...

The trick is, you need to go into Settings -> Airport Utility and enable the WiFi Scanner option

This option enables a very good WiFi scanner

Which shows both the channel and signal strength of every WiFi network your device can hear

On MacOS X, hold down (I forget which modifier key, possibly option?) and click the WiFi icon to get the same kind of info

For Windows or Android, I don’t know of an easy way to get the same information... if you do please let me know!

(And for Linux I assume you know what you’re doing)

Update: for Android, WiFi Analyzer seems to do the trick (thanks @PointZeroOne ) https://twitter.com/PointZeroOne/status/1246300289172299777