Wirebook › Lesson 7 of 18
Why does Wi-Fi get weaker through walls?
Your Wi-Fi is lightning in the kitchen, then the bars drop to one the moment you go to bed and shut the door. Is the door really blocking it? Mostly not. Let's build a tiny house, put a router in it and see what actually gets in the way.
Wi-Fi is radio, just very fast
Your router talks to your phone with radio waves, the same kind of invisible wave as an FM radio station, only wiggling much faster: about 2.4 billion or 5 billion times a second. That's what 2.4 GHz and 5 GHz mean. Each wiggle is one wave, and a 2.4 GHz wave is about 12.5 cm long, about the length of a pencil. A 5 GHz wave is about 6 cm, about the length of your little finger.
Radio waves pass straight through lots of things that light can't, like plasterboard, wood and your sofa. But every time they go through something, a little of their energy is soaked up or bounced away. A strong signal can lose a lot and still be fine; a weak one, far from the router, can't spare much.
So what really blocks it?
- Distance, first of all. The signal spreads out like ripples in a pond, so it fades quickly. Twice as far away can mean several times weaker indoors, even with nothing in the way.
- Heavy, dense walls. Brick and especially concrete soak up far more than a plasterboard wall. Old houses with thick walls are famous Wi-Fi traps.
- Metal reflects it. A fridge, a radiator, a mirror (they have a metal coating) or foil-backed insulation acts like a wall the waves bounce off. Behind them is a "radio shadow".
- Water soaks it up. Waves at these speeds are good at making water molecules jiggle, which is roughly how a microwave oven works too (at a much, much higher power). Fish tanks, and even people, take a bite. A crowd absorbs a surprising amount.
- Other radios. Neighbours' Wi-Fi, baby monitors, Bluetooth and a running microwave oven all share the 2.4 GHz band and can drown your signal out. It isn't blocked, just noisy. Does a microwave "eat" Wi-Fi? No: its metal box keeps almost all its power inside, but the tiny bit that leaks is right on the 2.4 GHz band, so nearby Wi-Fi gets shouted over while it runs. Switch it on in the house above.
2.4 GHz or 5 GHz?
Most routers send both. The longer 2.4 GHz waves get through walls better and reach further, but the band is crowded and slower. The shorter 5 GHz waves carry much more data, so they're faster, but walls cost them more. A good rule: 5 GHz in the same room or next door, 2.4 GHz when you're far away. Switch bands in the house above and you'll see the colours shrink at 5 GHz.
Fixes that actually help
- Move the router up and to the middle. Not in a cupboard, not on the floor behind the TV, not next to the fridge. Up high and central lets the signal reach every room with the fewest walls in the way.
- Add a mesh booster halfway. A second Wi-Fi box placed between the router and the weak spot repeats the signal. Put it where the signal is still good, not in the dead zone itself.
- Use a cable for things that don't move, like a games console or TV. A cable has no walls to fight.
- Pick the right band (see above), and restart an old router once in a while.
Bonus: let visitors join without typing the password
Phone cameras can join a network straight from a QR code. The code just holds one line of text, like WIFI:T:WPA;S:Cafe Guest;P:latte2026;;, which is the network's name and password. Make one with the free Wi-Fi QR code maker, which draws it right in your browser so the password is never sent anywhere, and print it for guests. Best on a separate guest network, because anyone who can see the code can join. How Wi-Fi QR codes work.
Grown-up fix-it guides: Wi-Fi connected but no internet · 2.4 GHz vs 5 GHz · find a saved Wi-Fi password.