Wi-Fi that will not reach upstairs, the back bedroom or the garden office is usually a coverage problem rather than a broadband problem, and the most common cause of all is simply where the router is sitting. Answer a few questions and this will tell you the most likely cause, what would confirm it, and how to fix it starting with the things that cost nothing.
Nothing is scanned and nothing is stored. It all runs in your browser, from the answers you tick.
Optional, but it settles the biggest question of all. Stand next to the router and run a broadband speed test on your phone: your provider's own app has one, and so does any speed test site. The number you pay for is on your bill or in your account. Leave both blank if you would rather not.
Mesh, in almost every case where you have a choice. A plug-in extender repeats the signal it receives, and on a single-band repeat it roughly halves the speed for everything connected to it, while usually creating a second network name your phone clings to long after you have walked away from it. A mesh system keeps one network name, hands your devices over as you move, and the good ones carry traffic between the units on their own channel. An extender is only really the right answer when you need to cover one spare room cheaply and you do not care much about speed there.
Almost always the router's position rather than the broadband. Wi-Fi comes out of the router in roughly a doughnut shape, not a beam, and it is absorbed by every floor, wall and chimney breast on the way. A router sitting in a hallway cupboard by the front door is already firing half its signal into the street before it starts on the stairs. Moving it somewhere central, out of the cupboard and off the floor, fixes a surprising number of upstairs problems for nothing.
Sometimes, and it is worth knowing why it often does not. A booster can only rebroadcast what it receives, so it has to sit somewhere the signal is still decent, roughly halfway to the dead spot rather than in it. Put one in the weak room and it will faithfully rebroadcast a weak signal. If the dead spot is behind a solid wall or across the garden, no amount of boosting fixes it and you want a cable and an access point instead.
Run a speed test standing next to the router, then run the same test in the room where it is bad. If it is slow in both places, the problem is the line or the router and no amount of Wi-Fi kit will help; that is a conversation with your provider. If it is fast at the router and slow in the room, the line is fine and you have a coverage problem, which is fixable.
Yes, and this is the one case where the cheap options genuinely do not work. An extender pointed down the garden will drop every time the weather turns. The proper fix is a cable out to the building, or a point-to-point wireless link where digging is not an option, with an access point at the far end. Done that way the outbuilding gets a real connection rather than one bar.
Often not. The most common causes are the router being in a bad spot, an old router the provider will replace free if you ask, and devices sticking to the wrong band. All three cost nothing. This tool tries the free explanations first and will tell you plainly when it thinks you do not need to spend anything. Where it genuinely does need hardware or a cable run, it says that too.
No. Nothing is scanned, measured or sent anywhere. It works entirely from the answers you tick, in your browser, and nothing is stored. It is the same set of questions I would ask you on the phone before coming out.
This is a guide based on the questions I would ask before coming out, not a measurement of your network. If it points at a free fix, try that first. Related: why does my wi-fi keep dropping, the repair or replace calculator if the problem turns out to be one ageing device, and Wi-Fi setup and home networking in Bolton if you would rather it was just sorted.