What this tool helps you work out
Radio signal falls as distance increases and can lose much more energy when it passes through walls, floors, metal or low-emissivity glass. The calculator combines free-space loss with the obstruction values you enter.
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Before you begin
Material losses are approximate. Two plasterboard walls are not necessarily identical, and reflections can strengthen or weaken a signal at different points in the same room. Use the result to compare locations, then verify with a survey.
Use measured values where possible and leave headroom for busy periods, overhead and future growth.
How the result is worked out
Free-space path loss is based on frequency and distance. Additional dB losses are then added for the selected obstacles. Because decibels are logarithmic, another 3 dB represents roughly half the received power, although usable data rate depends on more than power alone.
Worked example
At the same distance, a 5 GHz path has more free-space loss than a 2.4 GHz path. Adding a solid wall and a floor may turn a reliable nearby connection into a marginal one, which is why moving an access point by a few metres can outperform buying a more expensive client device.
Practical tips
- Compare several candidate access-point locations rather than trusting one estimate.
- Avoid placing access points beside large metal objects or inside cabinets.
- A stronger signal does not remove channel congestion.
- Use wired backhaul to avoid spending wireless capacity relaying traffic.
How signal strength is measured, and what the numbers mean
Wi-Fi signal strength is quoted in dBm — decibels relative to one milliwatt — and the numbers are negative because the received signal is a tiny fraction of a milliwatt. Closer to zero is stronger. The scale is logarithmic, which is the part that catches people out: every 3 dB lost halves the power, and every 10 dB lost divides it by ten.
| Signal | What to expect |
|---|---|
| −30 to −50 dBm | Excellent. Full speed, right next to the access point. |
| −50 to −60 dBm | Very good. Everything works, including video calls and 4K streaming. |
| −60 to −67 dBm | Good. Reliable for most uses. −67 is the usual design target for voice and video. |
| −67 to −70 dBm | Workable but reduced. Browsing and email fine, streaming may buffer. |
| −70 to −80 dBm | Poor. Slow, unreliable, drops under load. |
| Below −80 dBm | Effectively unusable, though the device may still show a connection. |
A strong signal in a noisy environment performs worse than a moderate signal in a quiet one. What actually matters is the margin between your signal and the background noise, and in a block of flats with twenty competing networks that margin can be poor even at close range. A device showing four bars and behaving badly is usually a congestion problem, not a coverage one.
What building materials do to a signal
These are indicative figures for a single obstruction. They vary with thickness, moisture content and construction, and they compound: two brick walls cost roughly twice one.
| Obstruction | Loss at 2.4 GHz | Loss at 5 GHz |
|---|---|---|
| Plasterboard partition | 2–4 dB | 3–5 dB |
| Wooden door | 2–4 dB | 3–6 dB |
| Interior brick wall | 4–8 dB | 6–12 dB |
| Solid external wall | 8–15 dB | 12–25 dB |
| Concrete floor | 10–20 dB | 15–30 dB |
| Glass window | 2–3 dB | 3–6 dB |
| Metal-backed insulation or foil-lined plasterboard | 20–40 dB | 25–50 dB |
| Mirror or metal appliance | 10–20 dB | 15–30 dB |
Two things on that table matter more than the rest. Foil-backed insulation, increasingly common in renovated and new-build homes, is close to a Wi-Fi mirror — it is a frequent explanation for a room that should have coverage and does not. And water absorbs 2.4 GHz strongly, which is why a large fish tank, a hot water cylinder or a full bath can put a shadow across a room.
Choosing between the bands
The trade-off is straightforward: lower frequencies travel further and penetrate better, higher frequencies carry more data and face less interference.
- 2.4 GHz reaches further and through more walls, but has only three non-overlapping channels in practice, and shares the band with Bluetooth, microwave ovens, baby monitors, cordless phones and every neighbouring network. In a terrace or a block of flats it is often unusable at any distance.
- 5 GHz has far more channels and much less congestion, and carries considerably more data — but loses roughly twice as much signal to each wall, and does not travel as far in open air either.
- 6 GHz, on Wi-Fi 6E and Wi-Fi 7 equipment, has a great deal of clear spectrum and almost no legacy congestion, at the cost of shorter range again. It is excellent in the same room and poor through masonry.
The practical answer for most homes is to run all available bands under one network name and let devices choose, then add a second access point rather than trying to force one to cover everything. Distance is a much cheaper problem to solve with another access point than with more power.
Fixing poor coverage, cheapest first
- Move the router. Free, and frequently sufficient. Central, high, out in the open, away from metal, mirrors, water tanks and the back of a television. A router in a cupboard by the front door is covering the neighbour's garden more than the back bedroom.
- Change channel. Also free. On 2.4 GHz use 1, 6 or 11 and nothing else — the intermediate channels overlap and make matters worse for everyone. On 5 GHz, pick something the neighbours are not on.
- Add an access point on a cable. The reliable answer. A second unit connected by Ethernet, or over existing coaxial or telephone wiring with the right adapters, gives full performance where it is placed.
- Mesh, if cabling is impossible. Convenient, and it works — but a mesh node repeating over wireless has to receive and retransmit everything, roughly halving throughput unless the system has a dedicated backhaul radio.
- Powerline adapters as a fallback. Performance depends entirely on the house wiring and is unpredictable; they work well in some houses and barely at all in others.
- Range extenders last. They are the cheapest option and the worst, halving throughput and often creating a second network that devices cling to at the wrong moment.
Frequently asked questions
What is a good Wi-Fi signal level?
There is no universal boundary, but around −67 dBm is often treated as a useful design target for reliable general data and calls. Actual client needs vary.
Why do dBm values use negative numbers?
Received Wi-Fi power is far below one milliwatt. A value closer to zero is stronger, so −50 dBm is stronger than −75 dBm.
Does 5 GHz always have less range?
It normally suffers more path loss at the same distance and may penetrate some obstacles less effectively, but antenna design, power limits and the environment also matter.
Can a Wi-Fi booster fix signal loss?
It may extend reach, but a poorly placed wireless repeater can reduce capacity. A correctly positioned wired access point is generally more predictable.
Why does signal change when people move around?
Bodies absorb and reflect radio energy, and movement changes the multipath environment.
What signal strength do I actually need?
−67 dBm is the usual design target for anything real-time, such as voice and video calls, and it is the figure professional surveys work to. Ordinary browsing and email remain usable down to about −75 dBm. Below −80 dBm a device may still show as connected while being effectively unusable, which is why a connection can appear present and do nothing.
Why does my phone show full bars but the internet is slow?
Bars indicate signal strength between the phone and the access point, and nothing else. They say nothing about congestion on the channel, interference from neighbouring networks, how many devices are sharing airtime, or whether the broadband connection behind the router is the actual constraint. Strong signal with poor performance almost always means congestion or a bottleneck further along.
Is 5 GHz always better than 2.4 GHz?
In the same room, generally yes — more capacity and far less interference. Through walls or at distance, no: 5 GHz loses roughly twice as much signal per obstruction. The sensible arrangement is to have both available under one network name and let each device pick, rather than choosing one for the whole house.
Will a more powerful router fix a dead spot?
Rarely, and less than the marketing implies. Transmit power is limited by regulation, so there is little room for a router to be meaningfully more powerful. There is also a asymmetry that gets overlooked: even if the router shouts louder, your phone's reply is transmitted at the same modest power it always was, so the return path stays weak. Moving the access point closer, or adding a second one, addresses both directions.
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References
Official guidance and standards can change. Check the linked source when applying the result to an important network.