WiFi Signal Strength Explained: RSSI, dBm and Better Coverage

Weak WiFi can be frustrating because it rarely fails in the same way everywhere. A connection may seem fine beside the router, then slow down, buffer or drop completely in another room, office, holiday home or outside area.

Signal strength is one of the first measurements used to understand the problem. It is commonly shown as a negative dBm number and often described as RSSI. The closer the reading is to zero, the stronger the received signal — so -55 dBm is stronger than -75 dBm.

That number is useful, but it is not the whole story. Interference, channel use, background noise, building materials, access-point placement, connected devices and the speed of the internet connection all affect the experience. These factors need to be considered together when planning an improvement.

What is a good WiFi signal strength?

The following ranges are a practical guide, not a guarantee. Different phones, laptops and WiFi adapters can report slightly different readings, and demanding applications need more headroom than basic web browsing.

For many professionally designed networks, around -67 dBm at the edge of the required coverage area is a useful starting target. It is not a universal pass mark. The correct target depends on the devices, applications, environment, noise level and roaming requirements.

Why are WiFi signal readings negative?

WiFi signal strength is commonly displayed in dBm, which measures received radio power relative to one milliwatt. The signal reaching a phone or laptop is a tiny fraction of a milliwatt, so the reading is normally negative.

The scale is logarithmic. A change of 10 dB represents a tenfold change in received power. That is why the difference between -60 dBm and -70 dBm can be much more noticeable than the numbers first suggest.

The simple rule is: closer to zero means stronger.

RSSI and dBm: are they the same?

Not exactly.

RSSI stands for Received Signal Strength Indicator. It is a relative indication created by the WiFi hardware, and manufacturers do not all calculate or display it in exactly the same way.

dBm is an absolute unit of received power. Many WiFi systems and measurement apps present their signal reading in dBm while also calling it RSSI. In everyday troubleshooting the terms are often used together, but it is best to compare results from the same device and measurement tool.

This is also why the WiFi bars on two different devices may not agree.

A strong signal does not always mean fast WiFi

Signal strength answers one question: how much of the access point’s radio signal is reaching the device? It does not prove that the connection is clean, uncongested or fast.

WiFi can still perform badly with a strong signal because of:

• Interference: neighbouring WiFi networks and non-WiFi equipment can compete with or disrupt the signal.
• Channel congestion: too many devices or access points sharing airtime can slow everyone down.
• Background noise: a useful signal needs to be sufficiently stronger than the noise around it. This is measured as signal-to-noise ratio, or SNR.
• Poor access-point placement: hiding a router in a cupboard, behind a television or at one end of a building can create avoidable weak areas.
• An unbalanced link: an access point may be powerful enough to reach a phone even when the phone cannot transmit reliably back to it.
• Internet or network limitations: a slow broadband connection, faulty cable, overloaded router or upstream service issue can look like a WiFi problem.

This is why a speed test on its own cannot diagnose WiFi coverage, and why adding a more powerful router is not always the right answer.

What weakens a WiFi signal?

Every building changes the way radio signals travel. Common causes of attenuation and coverage problems include:

• distance from the router or access point;
• thick stone, brick or reinforced concrete walls;
• metal cladding, foil-backed insulation and underfloor heating materials;
• mirrors, appliances, plant rooms and large metal objects;
• people, water and changing occupancy levels;
• poor antenna position or orientation;
• trying to cover several floors or separate buildings from one location;
• relying on an outdoor access point to serve the inside of a metal caravan or holiday home.

These issues are particularly relevant across North Wales, where older stone properties, converted buildings, rural sites, farms, caravan parks and holiday accommodation can present very different RF challenges. A design that works in a modern open-plan office may perform badly in a property with thick internal walls or metal construction.

2.4 GHz, 5 GHz and 6 GHz coverage

The strongest-looking network is not automatically the best choice. Each WiFi band has different characteristics.

2.4 GHz

2.4 GHz generally travels farther and penetrates obstacles better than the higher bands, but it has fewer non-overlapping channels and is often busier. It can be useful for range and some low-bandwidth devices, but congestion can limit performance.

5 GHz

5 GHz offers more channel capacity and is commonly the better choice for modern phones, laptops, streaming and business use. Its signal normally weakens more quickly through dense materials, so good access-point placement matters.

6 GHz

6 GHz, available with compatible WiFi 6E and WiFi 7 equipment, offers additional spectrum and can provide excellent performance in the right design. Its useful coverage is more easily reduced by walls and it requires compatible client devices.

A well-designed system uses the bands deliberately instead of simply enabling every option at maximum power.

How to check your WiFi signal properly

A quick reading from a phone or laptop can identify an obvious dead spot, but use it as an indication rather than a final diagnosis.

For a more useful home or business check:

1. Use the same device and measurement app throughout the test.
2. Check the places where WiFi is actually needed, not only beside the router.
3. Test both stationary use and movement between coverage areas.
4. Record the signal level, band and access point as well as speed, latency and dropouts.
5. Repeat the test when the property or business is busy.
6. Note physical obstacles such as stone walls, metal structures and separate buildings.

Avoid changing minimum-RSSI, transmit-power or roaming settings based on one reading. An aggressive threshold can disconnect devices without giving them a better access point to use.

Practical WiFi installation and improvement

WiFiSetup focuses on practical installation and network improvement work. We help get connectivity into places that do not currently have it and improve existing links that are limiting coverage or reliability. Depending on the property or site, this can include:

• installing access points where WiFi is actually needed;
• extending service into rooms, buildings, static caravans and outdoor areas;
• improving backhaul with suitable 5 GHz or 60 GHz wireless links;
• connecting separate buildings or remote parts of a site;
• improving access-point placement, cabling and network equipment;
• replacing unreliable or unmanaged equipment with a system that can be supported;
• planning sensible upgrades around the layout, existing infrastructure and available budget.

The aim is straightforward: provide a stable connection where one is needed or improve the weakest part of an existing installation. We will explain the practical options clearly and say when a problem needs specialist testing outside the work we provide.

When to discuss WiFi improvements

It is worth getting in touch when:

• a room, building, caravan or outdoor area has little or no useful coverage;
• a separate building or remote part of a site needs a network connection;
• an existing wireless backhaul link is unreliable or needs more capacity;
• a holiday park, guest property or business receives repeated WiFi complaints;
• unmanaged extenders or repeaters have been added without solving the underlying problem;
• you are planning access points, cabling or backhaul for a new area;
• an existing installation needs a practical upgrade or extension.

WiFiSetup provides practical WiFi advice, installation and managed network support across North Wales and beyond. We work with homes, businesses, hospitality venues, holiday accommodation, caravan parks and rural sites.

Frequently asked questions

Is -67 dBm a good WiFi signal?

It is commonly used as a design target for reliable voice, video and roaming when the signal-to-noise ratio is also healthy. It should be treated as a useful benchmark, not a guarantee for every device or environment.

Is -70 dBm bad?

-70 dBm is often usable for email and web browsing, but it provides less margin for video calls, streaming, roaming and busy networks. If the channel is noisy or congested, performance may be poor even at this level.

Why is my WiFi slow when I have full signal bars?

The bars show only a simplified view of received signal strength. Interference, congestion, an overloaded router, a slow internet connection, packet loss or a faulty network link can all cause poor performance despite a strong signal.

Can I use a WiFi booster or repeater on a managed network?

On a WiFiSetup-managed network, no. We do not condone unmanaged signal boosters, repeaters or privately installed mesh and extender devices. Because this equipment sits outside the managed system, we cannot control its channel selection, transmit power, firmware or roaming behaviour, and we cannot verify the quality of the connection it is receiving.

A repeater installed where the original signal is already weak can rebroadcast that poor connection to other users. It may also consume additional airtime, create overlapping RF energy and encourage devices to connect through a path that cannot provide a reliable service. The result can be worse performance for the person using the repeater and for other customers nearby. This is a common driver of WiFi complaints on caravan sites.

These devices are usually installed with good intentions, but when they are not part of the managed design or visible to the network controller they can unintentionally make the wider network harder to support. If coverage is poor, report the location, affected device and approximate time of the problem. The managed system can then be checked and the correct remedy considered, such as adjusting the existing installation or adding an appropriately positioned managed access point with a suitable backhaul connection.

Should I turn the router power up to maximum?

Not automatically. High access-point power can make a network appear to cover a larger area even though phones and other client devices cannot transmit back at the same power. It can also create oversized cells and poor roaming in multi-access-point systems.

Can outdoor WiFi provide reliable coverage inside a caravan?

Metal caravan and holiday-home construction can severely weaken radio signals. Reliable indoor service often needs an indoor access point or a properly designed connection into the unit. The practical options depend on the construction, existing coverage and the cabling or backhaul available at the site.