Why your Wi-Fi is slower than your internet

A customer buys a 50Mbps line, runs a speed test on their phone and gets 48Mbps. Then they sit in the lounge and a video keeps dropping to standard definition. Nothing about the connection changed.

The line was never the problem. What happens between the router and the device is, and it is where most of the disappointment with a perfectly good connection comes from.

This is what is actually going on.

Your 50Mbps is shared, not handed out

This is the misunderstanding underneath most of the others.

A 50Mbps service is one pipe into the house, shared by everything using it at that moment. It is not 50Mbps to each person, each device or each room.

Picture a normal evening. One person is downloading a large game update on a console, which will happily consume the entire line given the chance. Somebody else is streaming in 4K. A third is in a video call for work. A fourth is scrolling on a phone.

That is four things drawing from one 50Mbps supply. The video call does not fail because the connection is broken. It fails because a download is winning the competition for a shared resource, and the call is the thing that notices first, because a video call is far less tolerant of a delayed packet than a download is.

This is why “my internet is slow” and “the speed test says 48Mbps” can both be true at once. The pipe is delivering what it promised. The problem is what is trying to fit through it simultaneously.

Two things follow from that, and neither of them is “buy a faster line.”

The first is that a faster line genuinely helps when the contention is real, meaning several heavy users at once. The second is that a lot of the time the contention is not the line, it is the Wi-Fi. And that is where the numbers get interesting.

What a wall actually costs you

A Wi-Fi signal loses energy as it passes through matter, and the amount depends on the material and the frequency.

Here is a published set of figures for common building materials.

Figures from Huawei WLAN planning guidance. The International Telecommunication Union publishes the underlying material model as ITU-R P.2040 if you want the physics rather than the table.

Read the third row against the second. A double brick wall costs 25dB on 5GHz. On 2.4GHz the same wall costs 15dB, and on 6GHz it costs 30dB.

Those numbers look catastrophic, and quoted as percentages they are. Decibels are logarithmic, so 25dB means about 99.7 percent of the signal power is lost, and 15dB means about 97 percent. Read without context that suggests one wall kills a connection. It usually does not, and it is worth understanding why.

What the decibels actually consume

A decibel loss is always relative to where you started, and the start is well above the floor.

Indoors, a 5GHz signal a metre or two from the router sits somewhere around minus 40dBm. A 5GHz link stays usable down to roughly minus 80 to minus 85dBm, depending on the device. That leaves about 40dB of headroom before things fall apart.

What that costs in practice looks like this.

One double brick wall hurts. It does not disconnect you. Two is usually where 5GHz stops being dependable. Three is where people say “there is no Wi-Fi in that room”, and they are right.

That is the whole argument for a mesh system, by the way. It is not that one wall is fatal. It is that the headroom runs out faster than the floor plan does.

The percentages are also per wall, and they do not sit evenly. Each wall takes its share of what is left, so it is the total against the starting level that decides whether a device works, not any single figure in the table.

This is also why the frequency your devices prefer is not always the one that reaches them. 5GHz and 6GHz are faster because they carry more data, and they are worse at getting through walls for exactly the same reason. A short wavelength packs more information and loses it faster when it meets an obstruction.

What this means in a South African house

Most houses here are built with double brick external and supporting walls, either facebrick or plastered, at around 240mm. Internal non load-bearing walls are usually single brick at around 120mm. Ceilings are gypsum board, sold here as rhinoboard, unless the building is a slab construction.

That combination is unforgiving, but the walls usually are not what breaks a link on their own.

Three single-brick internal walls cost 45dB on 5GHz. Against 40dB of headroom that is the point where a 5GHz device stops being reliable. On 2.4GHz the same three walls cost 30dB, which is why the older band keeps working in rooms where 5GHz gave up. It is slower and it travels further, and that trade is the whole reason both exist.

The outer wall is the one that catches people out. Put one double brick wall between the router and the garden and you have spent 25dB on 5GHz before the signal is even outside. On a patio that may be enough to lose the connection entirely, since the garden is past the wall rather than in the room beyond it. People expect Wi-Fi to reach the patio because it looks like open space. The wall does not care about the view.

Gypsum board is the one material that is cheap. At 3 to 4dB, a rhinoboard ceiling barely slows anything, which is why a well-placed access point in a ceiling void is such an effective answer in a single-storey house.

Where people put the router

Geometry matters as much as materials, and the placement mistakes are consistent.

Behind or beside a television. The TV is a large sheet of metal and glass with its own electronics radiating. It absorbs and reflects what should be reaching the rest of the room.

In a cupboard, or inside a TV cabinet. A wooden door costs 10 to 15dB on 5GHz before the signal has gone anywhere useful. Some cabinets are metal-backed, which is closer to a shutter door at 20dB.

Next to or facing a mirror. A large mirror is a sheet of silvered glass, which means a reflective surface tuned to exactly the frequencies being used. It does not absorb the signal so much as throw it back at the router, and it creates paths that interfere with the direct one.

On the floor, or low down. Furniture is in the way of everything at that height.

In the corner of the house. The corner is the worst place to put a transmitter that needs to cover the house, because half its output is leaving the building.

The general principle is that a router wants height, air and a central position, and anything large, dense or reflective close to it is costing coverage.

The router itself

A better router genuinely helps, sometimes a lot, and there are specifics to it.

Higher gain antennas push the signal further in the direction they favour, at the cost of the other directions. Useful, but not magic.

Wi-Fi 6 and Wi-Fi 7 handle many devices at once far better than older standards. This matters more than people expect. A house with phones, tablets, TVs, consoles, cameras and appliances is not short of bandwidth so much as it is crowding the air, and the newer standards were designed for that crowding. They help only if the device on the other end supports the same standard. The newest router paired with an older phone negotiates down to what the phone can do.

Gigabit ports instead of fast ethernet. A router with a 100Mbps port cannot pass more than 100Mbps however fast its Wi-Fi claims to be. This is a common and invisible bottleneck on cheaper hardware.

All of it can be true at once and none of it can fix a slow line. You can buy the best router available and connect it to a 10Mbps service, and you will have an excellent wireless network delivering a very slow internet connection. The router can only distribute what it is given.

What actually fixes it

Work through these in order, because the earlier ones cost nothing.

Move the router. Out of the cupboard, off the floor, away from the television and any large mirror, and as central and as high as the cable will allow. This is free and it solves more complaints than anything on the list.

Fix the line first if the line is the problem. Run a speed test with a cable connected directly to the router, not over Wi-Fi. If that gives you the speed you pay for, the line is fine and everything after this point is about Wi-Fi.

For most houses, one router in one place is not enough. A mesh system, or additional access points, puts the signal closer to where it is used rather than trying to force it through walls. In a house with double brick supporting walls and a long floor plan, this is usually the answer rather than a stronger router.

We sell whole-home mesh systems and upgraded routers in the store, and we are not going to pretend that is the answer to every problem. A well-placed router you already own beats a badly-placed one you just bought.

Then look at the line. If everyone is home, everyone is streaming and someone is downloading, a faster service genuinely helps. That is a real contention problem, and it is the case where upgrading does what you want. But do it after the free fixes, not before.

The short version

A video call dropping out while somebody else downloads a game is not a broken line. It is a shared resource being asked to do too much at once, over a wireless link that may already be down to a fraction of its headroom because of where the router sits. Contention finishes off a connection that was already weak, and the call is the first thing to notice.

Test the line with a cable. Move the router. Add mesh if the house is spread out. Then decide whether the service itself is the constraint.

If you are not sure which of these is your problem, log a fault and describe what is happening rather than just that it is slow. Knowing whether a device is far from the router, and how far, tells us most of what we need before anyone looks at the line.