How to make a WiFi heatmap
A WiFi heatmap shows signal strength across a floor plan, so you can see at a glance where coverage is weak. This guide walks through making one with WiFi Heatmapper, from an empty page to an exported image.
Updated
A first heatmap takes about two minutes: add a plan, take a few readings, and the map draws itself. Covering every room of a flat takes a few minutes more, mostly walking. Everything happens in the browser and nothing is uploaded.
What you need
- A floor plan image in PNG or JPEG. A blueprint, a photo of a hand-drawn sketch or a screenshot from a listing all work. If you have nothing, you can sketch the walls in the app.
- A laptop connected to the Wi-Fi you want to check. Macs, Windows and Linux can all show signal strength in dBm, which is what you will type in.
- Optional: a phone or tablet to place points while you walk. iPhones do not show signal strength in dBm, so the reading itself should come from the laptop.
1. Add your floor plan
Open WiFi Heatmapper and drop your image onto the page, or choose Sketch one instead to draw walls on a grid. If the plan is sideways, rotate it in the plan step. The plan only has to be roughly right: what matters is that you can tell where you are standing.
There is also a scale step, where you click both ends of something you know the length of. You can skip it. It is only used to set a realistic walking pace for guided walks.
2. Take readings
Stand somewhere, click that spot on the plan, and type the signal strength your laptop shows. A crosshair marks the reading and the heatmap updates immediately.
Where to find the signal strength
| System | How to read it |
|---|---|
| macOS | Hold Option and click the Wi-Fi icon in the menu bar. Use the RSSI value, for example -58. |
| Windows | Run netsh wlan show interfaces in Command Prompt. Use the Rssi value if it is listed. Otherwise type the Signal percentage with a % sign, for example 80%, and the app converts it approximately. |
| Linux | Run iw dev to find the interface name, then iw dev wlan0 link with that name. Use the signal value. |
Where to measure
- Start next to the router, so you know what the best case looks like.
- Take at least one reading in every room, plus the places you actually use Wi-Fi: the desk, the sofa, the bed, the meeting room table.
- Add readings in doorways, at the far corners and on the far side of thick walls. That is where coverage usually breaks down.
- In open spaces, a reading every 3 to 5 meters is plenty. Closer spacing rarely changes the picture in a home.
Getting readings you can trust
- Hold the laptop the way you normally use it. A laptop on the floor or with the lid half closed reads lower.
- The value moves by a few dBm from second to second. If it jumps around, wait a moment and type a typical value instead of the best one.
- If your router uses the same network name for 2.4 GHz and 5 GHz, the laptop can switch between them as you walk, and 2.4 GHz usually shows a stronger number. Note which band you are on (the Option-click menu on a Mac shows the channel) and keep it consistent.
3. Read the heatmap
Green is strong and red is weak. The colors fade the further a spot is from your nearest reading, so pale areas are not weak signal: they are places you have not measured yet. Add a reading there before drawing conclusions. Hover anywhere on the plan to see the estimated value at that spot.
| Signal | Rating | What it means in practice |
|---|---|---|
| -50 dBm or better | Excellent | Fast and stable everywhere it reaches. Typical within a few meters of the access point. |
| -60 to -50 dBm | Good | Reliable for everything, including calls and HD streaming. |
| -67 to -60 dBm | Fair | Fine for browsing and streaming. -67 dBm is the common minimum for voice calls. |
| -75 to -67 dBm | Weak | Usable, but calls may stutter and speeds drop. |
| -85 to -75 dBm | Poor | Slow and drops out. Treat these spots as dead zones for practical use. |
| below -85 dBm | Unusable | Little or no usable connection. |
Between readings, the map is an interpolation: a smooth estimate from the nearest measurements. It is a good guide to where the weak areas are, but only the crosshairs are measured values. For more on dBm and what counts as a dead zone, see What is a WiFi heatmap?
4. Export it
Export the heatmap as a PNG to keep it, share it, or compare it with a second survey after you move the router. Free exports carry a WiFi Heatmapper watermark.
Common mistakes
- Too few readings. A handful of readings already draws a heatmap, but not a reliable one. Every room needs at least one.
- Measuring from one spot. Each reading has to be taken where you click. Walking back to the desk to read the value and then clicking a far room gives a misleading map.
- Mixing bands. Readings from 2.4 GHz and 5 GHz on the same map make a weak 5 GHz area look fine.
- Treating colors as speed. Signal strength is coverage, not throughput. A strong signal on a congested channel can still be slow.
Next step: fix the weak spots
Once you know where the signal is weak, try a different router position, a mesh node or an extra access point, then measure again and compare. The small office placement guide walks through that loop.