Wi-Fi Signal Strength Explained: The dBm Chart That Actually Means Something

Every Wi-Fi guide throws numbers at you — -67 dBm, -80 dBm — without saying what they buy. A number is only useful if you know what breaks on either side of it.

Here is the scale with the consequences attached: what each level actually supports, why the gap between two readings is not what your intuition says, and why the same number means two different things in a house and in an apartment block.

Why the number is negative#

dBm means decibels relative to one milliwatt. Zero dBm is exactly 1 milliwatt. Everything a Wi-Fi client receives indoors is a tiny fraction of a milliwatt, so every reading you will ever see is negative.

A home router transmits at roughly 20 dBm — about 100 milliwatts. By the time that signal has spread through a couple of rooms and crossed two walls, your phone might be receiving -70 dBm, which is around 0.0000001 milliwatts. The signal has not been damaged; it has just spread out and been absorbed.

Two consequences worth fixing in your head:

• Closer to zero is stronger. -45 dBm is far better than -75 dBm.
• The scale is compressed on purpose. The strongest reading in a house and the weakest usable one are about a million to one apart in raw power. Decibels are what make that fit on a chart.

The dBm chart, -30 to -90#

Read this as bands, not as exact cutoffs. A device's behavior at -68 dBm depends on the noise around it, the band, and how good its antenna is.

The practical dividing line most people care about is -67 dBm. Above it you have margin; below it you are spending your remaining headroom on retries. It is also the number that defines where an extender belongs — see where to place a Wi-Fi extender.

What each activity actually needs#

Video calls and gaming show up higher on that list than their bandwidth suggests, because they care about consistency rather than volume. A link at -72 dBm can average 40 Mbps and still ruin a call, because the retries arrive as jitter.

Why -70 is not twice as bad as -35#

Decibels are logarithmic, and that trips up almost everyone.

• 3 dB is half the power. -63 dBm is half the received power of -60 dBm.
• 10 dB is one tenth of the power. -70 dBm is one tenth of -60 dBm.
• So -35 dBm to -70 dBm is 35 dB, which is roughly 3,000 times less power — not "twice as bad".

But throughput does not follow power in a straight line either, which is why the raw ratio is also misleading in the other direction. Radios pick from a ladder of modulation rates, and each step down is a discrete drop:

• Between about -40 and -60 dBm you often lose almost nothing. The radio is already at or near its top rate and has margin to spare.
• Between about -67 and -80 dBm throughput falls off a cliff. Each rung down the ladder can halve your speed, and retransmissions eat airtime on top of that.

That is why one extra wall can turn a perfect room into a bad one while doubling the distance across an open living room barely registers. Losing 6 dB in the -50s costs you nothing you would notice. Losing the same 6 dB in the -60s can cost you half your speed. The per-material numbers behind that are in how walls affect Wi-Fi.

RSSI is only half the answer: SNR#

RSSI is what your device hears from the router. It says nothing about everything else your device hears at the same time.

Signal-to-noise ratio is the difference between them, in plain dB:

SNR = signal (dBm) - noise floor (dBm)

A -65 dBm signal in a quiet house with a -95 dBm noise floor gives you 30 dB of SNR: excellent. The same -65 dBm signal in an apartment where the noise floor has been pushed to -75 dBm by a dozen neighboring networks gives you 10 dB: effectively unusable. Identical RSSI, opposite outcomes.

This is the single most common reason a strong-looking room performs badly, and it is why apartments behave so differently from detached houses. Finding a quieter channel to sit on is a separate job, covered in what your neighbors' networks are doing to your noise floor.

How to read RSSI on your own devices#

Pick whichever of these you have. All of them give you a real number rather than an icon.

1. Mac (best free option). Hold Option and click the Wi-Fi icon in the menu bar. You get RSSI and noise, both in dBm. Subtract them for SNR. This is a genuine meter and it is already installed.
2. Android. Settings, then Network and internet, then Wi-Fi, then tap the connected network or its gear icon. Some manufacturer builds only show a word like Good, in which case a Wi-Fi analyzer app will read the same OS-provided RSSI and show the number.
3. iPhone and iPad. iOS does not expose the connected network's RSSI to third-party apps, so no App Store analyzer can show it. Apple's own AirPort Utility app can, once you turn on its Wi-Fi Scanner switch inside the iOS Settings app, and that scanner reports RSSI for the networks it sees.
4. Any router. Open the router's admin page or app and find the client list. Most list a signal level per connected device. That is the level the router hears from your phone rather than the reverse, but in practice the two are usually within a few dB.
5. Windows. Run netsh wlan show interfaces in a terminal. It reports signal as a percentage, not dBm; dividing the percentage by two and subtracting 100 gets you an approximate dBm value.

When you take a reading, stand still, hold the device where you actually use it, and wait a few seconds. Readings swing 3 to 5 dB just from your body position and someone walking past.

Turning a number into a decision#

The point of a reading is to choose what to do next. Take it in the room that fails, at the height you use it.

• Better than -60 dBm and still slow. Signal is not your problem. Look at congestion, the device, or your internet connection — start with full bars but still buffering. An extender here will change nothing at all.
• -60 to -67 dBm. Comfortable for most things. This is also the window you want at the extender's own location, because that device needs a clean link back to the router.
• -68 to -74 dBm. Marginal, and a real coverage gap. Move the router first, since that is free, then consider a second radio.
• -75 dBm and below. Poor, and by -85 dBm effectively dead. An extender only helps if some point between the router and this room reads -60 to -67 dBm — otherwise there is nothing worth repeating and you want a wired access point. The full diagnosis is in what turns a room into a dead zone.

Getting the numbers without walking the house#

One reading describes one spot. Choosing where a router or an extender should go means knowing the level in five spots at once — including spots where nothing is plugged in yet, which no meter can tell you.

That is the gap Range Up's coverage simulation fills, and it is what the placement method that uses these numbers runs on. Draw the floor plan, set the material preset to match how the place is built, stand the router where it really stands, and you get a predicted level for every room at once instead of one number from wherever you happened to hold the phone; how to read the heatmap covers what the colors are saying. Because those levels are computed rather than sampled, hypotheticals are fair game: drag the router marker onto a different shelf, or name a room and have the app reveal the spot a second radio should occupy for it.

Every level it shows is predicted from your layout, never measured off your live network — which is the whole point, because the hardware you are weighing up is not in the house yet. Get the app and draw the rooms you are unsure about.