WiFi signal loss through walls: attenuation by material
Typical attenuation in decibels for the materials you meet in real buildings, at 2.4, 5 and 6 GHz. Remember the scale is logarithmic: every 3 dB lost halves the signal power, and 10 dB cuts it to a tenth.
Rather not do this by hand? WiFi Weave applies these values automatically once you draw walls on your floor plan, and shows the resulting coverage as a heatmap.
Attenuation by material (dB)
| Material | 2.4 GHz | 5 GHz | 6 GHz | Notes |
|---|---|---|---|---|
| Plasterboard / drywall (single sheet) | 2–4 | 3–5 | 3–6 | The everyday interior wall; two sheets on a stud = roughly double |
| Interior hollow wall (2 sheets + studs) | 3–6 | 4–8 | 5–9 | Metal studs add more than timber |
| Wooden door | 3–4 | 4–6 | 5–7 | Solid hardwood sits at the top of the range |
| Plain glass window (single pane) | 2–3 | 3–4 | 3–5 | Ordinary glass is fairly transparent to RF |
| Low-E / tinted / coated glass | 8–15 | 10–20 | 12–25 | The metallic coating is the problem — modern offices are full of it |
| Cinder block / hollow concrete block | 4–8 | 6–12 | 8–14 | Filled cores push this much higher |
| Brick wall | 6–10 | 10–15 | 12–18 | Double-skin brick roughly doubles the figure |
| Solid concrete wall | 10–15 | 15–25 | 18–28 | Highly thickness dependent |
| Reinforced concrete (rebar mesh) | 15–25 | 25–35 | 28–40 | The mesh acts like a partial Faraday cage |
| Metal door / metal partition | 6–10 | 10–15 | 12–18 | Frames and gaps often leak more than the panel |
| Elevator shaft / metal enclosure | 20–30 | 25–40 | 30–45 | Treat as opaque; cover from inside if service is required |
| Filled bookshelf / stock racking | 2–6 | 3–8 | 4–10 | Warehouses change as stock moves — design for full racks |
| Human body | 3–4 | 4–6 | 5–7 | Matters in dense rooms; a full lecture hall is not an empty one |
Ranges, not constants. Thickness, moisture content, backing material and construction era all move these numbers — treat them as planning inputs and validate on site.
A worked example
An AP transmitting at 20 dBm serving a laptop 15 m away on 5 GHz, through one drywall partition and one brick wall:
- Transmit power+20 dBm
- Free-space path loss at 15 m, 5 GHz−70 dB
- Drywall partition−4 dB
- Brick wall−12 dB
- Received signal≈ −66 dBm
That scrapes past a −67 dBm voice target with nothing to spare — no margin for a closed door, a full room of people, or a client radio weaker than the AP. In practice you would move the AP or add one.
Common questions
How much WiFi signal is lost through a wall?
It depends entirely on the material. A single sheet of drywall costs roughly 2–4 dB at 2.4 GHz, while a reinforced concrete wall can cost 15–25 dB — and every 3 dB lost is half the signal power. That is why two buildings of identical square footage can need very different numbers of access points.
Why does 5 GHz penetrate walls worse than 2.4 GHz?
Higher frequencies have shorter wavelengths, which are absorbed and scattered more readily by dense material. As a rule of thumb 5 GHz loses noticeably more through the same wall than 2.4 GHz, and 6 GHz slightly more again. This is the trade you accept for wider channels and less congestion.
How do I use these numbers?
Start from the AP transmit power, subtract free-space path loss for the distance, then subtract the attenuation of every wall the signal crosses. Compare the result with the minimum signal your applications need — commonly around -67 dBm for voice and video. If the result is below target, you need another AP or a different position.
Are these values accurate enough to design from?
They are good enough for planning and for sizing a budget, which is what predictive tools use them for. They are not a substitute for validation: real construction varies, and a post-installation survey is what confirms the design. Use the ranges to plan conservatively, then verify.
Sources: ITU-R P.1238 (propagation data for indoor radio systems), published vendor RF design guides, and IEEE 802.11 deployment documentation. Figures are typical ranges for planning, not measured values for any specific building.
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