Signal strength, not speed tests
Speed tests measure your ISP connection plus WiFi plus server load, at one spot, at one moment. For diagnosing coverage, the metric that matters is signal strength (RSSI), measured in dBm. It isolates the WiFi link itself and is stable enough to compare between rooms.
| Reading | Quality | What it means in practice |
|---|---|---|
| -30 to -50 dBm | Excellent | Full speed, 4K streaming, anything |
| -50 to -60 dBm | Good | Solid for calls, gaming, streaming |
| -60 to -70 dBm | Fair | Browsing fine; video calls may stutter |
| -70 to -80 dBm | Poor | Slow, unstable, drops likely |
| Below -80 dBm | Dead zone | Effectively unusable |
How to measure room by room
You could walk around writing dBm numbers on a paper plan — that's genuinely how surveys used to be done. A heatmap app automates exactly that clipboard workflow:
- Load your floor plan into HeatFi (sketch it in a minute if you don't have one).
- Walk every room and tap Take Sample at the spots where you actually use WiFi — desk, bed, sofa, kitchen counter. Two or three samples per room is plenty.
- Read the results two ways: per-room signal scores for a quick ranking of best-to-worst rooms, and the interpolated heatmap for seeing why — which walls or distances kill the signal.
What to do with the numbers
- One bad room → placement fix or extender at the coverage edge: extender placement guide.
- Whole floor bad → vertical penetration problem: WiFi slow upstairs.
- Everything mediocre → the router position is wrong before anything else is: router placement.
- Good signal, bad speeds → band or ISP issue, not coverage: check the bands guide.
Repeat the survey after any change. Rooms don't lie on a before/after heatmap.
Quick answers
What is a good WiFi signal strength in dBm?
-50 dBm or better is excellent, -60 dBm is good for anything including calls, -70 dBm is where problems start, and below -80 dBm is effectively a dead zone.
How do I check WiFi signal strength in different rooms?
Use a heatmap app: load a floor plan, walk each room taking samples, and get per-room scores plus a colour-coded map. It's the same reading iOS/Android use internally, pinned to locations.
Why is my WiFi speed test fine but video calls drop?
A speed test at one moment can pass while marginal signal (-65 to -75 dBm) causes retransmissions and jitter that break real-time calls. Room-by-room signal measurements expose this; a single speed test won't.
See your WiFi instead of guessing
HeatFi turns your phone into a WiFi survey tool. Draw your floor plan, walk each room, and get a colour-coded heatmap in minutes. Free — no account needed.
