Guides / Diagnostics
What dBm means, and how to measure your own WiFi
5 min read
"Two bars" means whatever the phone manufacturer decided it means. There is a real measurement underneath, and anyone can read it.
The scale
WiFi signal strength is measured in dBm — decibels relative to one milliwatt. The numbers are always negative, and closer to zero means stronger. It is a logarithmic scale, so the gaps matter more than they look: every 3 dBm roughly doubles or halves the power.
| Reading | What you'll experience |
|---|---|
| −30 to −50 dBm | Excellent. You're near the access point. |
| −50 to −60 dBm | Good. Everything works, including video calls. |
| −60 to −67 dBm | Acceptable. This is the edge of the design target. |
| −67 to −75 dBm | Marginal. Calls drop, video buffers, files crawl. |
| Below −80 dBm | Effectively dead, even if a bar still shows. |
−67 dBm is the number to remember. It's the widely used threshold for reliable voice and video, and it's what a competent installer designs to in every room the customer cares about.
How to measure it yourself
Install a free scanner — WiFiman works on iPhone and Android. Then:
- Hold the phone at chest height, the way you actually use it. Readings taken up near the ceiling flatter the result and describe an experience nobody has.
- Stand still for five to ten seconds at each spot. The number bounces around; you want the value it settles at, not the first flicker.
- Walk a grid, not a path. Take a reading every ten to fifteen feet. Include hallways, corners, and the far side of the bed.
- Go outside. Patio, driveway, garage, any outbuilding. This is usually where the worst numbers hide.
- Write it on a floor plan. Sketch the layout, put the number in each room, then colour it in: green above −60, yellow to −67, red below. You now have a coverage map.
Also check how crowded the airwaves are
Signal strength is only half the story. A strong signal competing with twenty neighbours on the same channel still performs badly — like shouting in a crowded bar.
Most scanner apps include a channel view showing every nearby network and which channel it occupies. In a dense apartment building you may find thirty networks stacked on 2.4 GHz channels 1, 6 and 11. If your signal reads −55 dBm but everything is slow at night, congestion is your problem, and no amount of extra hardware fixes it. Changing channels or moving devices to 5 GHz does.
Test speed at the extremes
Run a speed test at your best spot and your worst spot. The gap is the useful part. "I pay for 500 Mbps and the back bedroom gets 6" is a far more persuasive fact than any dBm reading, and it tells you whether the problem is your internet plan or your coverage. If the best spot in the house is also slow, that's a provider problem. If only the far rooms are slow, that's a coverage problem, and a faster plan won't touch it.
Measure again after any change
Same phone, same app, same time of day, same spots. Different hardware reports different numbers, so a before-and-after comparison is only meaningful if the method stays identical. This is the single most common mistake people make when evaluating whether an upgrade helped.