[edent]

Here's the system I used.

How are the WiFi speeds when you're stood next to the router? If they're slow, your router is to blame.

How about the room next to your router? If they're slow, your walls are to blame.

In the first case - buy a better router.

In the second case - buy access points and run Ethernet to them.

WiFi isn't some magic, esoteric, unknowable force. It is radio waves.

You can get WiFi scanners for Android which will let you map your house, see signal strength, and SNR. But that won't give you much more information than the above two steps.

[PaulHoule]

… to be fair in the typical cheap setup people set up the WiFi router in the corner of the house that the cable comes in and wonder why the reception is bad on the other corner.

The minimum amount of Ethernet you can lay to improve performance (get over the idea that running Ethernet is something your grandad would have done back in the war) is from the place your network comes in to the center of your home, which increases the signal strength to the far corner 4x if you do the math.