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Wi-Fi signal strength (RSSI) explained: what dBm is good?
Last updated: 9 October 2026.
RSSI is the received signal strength, measured in dBm. The numbers are negative, and the closer to zero, the stronger the signal. The scale is logarithmic: every 3 dB roughly doubles or halves the power, and every 10 dB is a factor of ten. A move from -60 to -70 dBm therefore means one tenth of the power, not a small step.
What the numbers mean
| RSSI | Typical meaning |
|---|---|
| -50 dBm or stronger | Excellent, usually close to the access point |
| -50 to -60 dBm | Very good |
| -60 to -67 dBm | Good; common target for voice and video |
| -67 to -70 dBm | Fair; basic coverage |
| -70 to -80 dBm | Weak; slow or unreliable |
| Below -80 dBm | Usually unusable |
These are general guides. Requirements vary with devices, applications and interference.
RSSI is not the whole story: noise and SNR
A receiver needs the signal to stand clear of the noise. On a 20 MHz channel the noise floor is typically around -95 dBm, so a -65 dBm signal has roughly 30 dB of signal-to-noise ratio (SNR). The slowest data rates work with a few dB of SNR, while the fastest modulations need about 30 dB or more. That is why a target of -65 dBm is a sensible design value for demanding use, and why interference, which raises the noise, can ruin a design that looks fine on an RSSI map.
Design for the client, not only the access point
An access point may transmit at 20 dBm or more, but a phone or laptop transmits at roughly 15 dBm and has a smaller antenna. A client at the edge of a cell can hear the access point and still be unable to be heard. Signal Plan therefore balances access point power to a 15 dBm client plus the antenna gain each model's datasheet gives, instead of assuming maximum power. Raising power beyond that widens the downlink forecast but not the usable cell.
Where the dBm figure comes from
The predicted RSSI at a point is the access point's EIRP, minus the free-space loss at 1 m for the band (40.2, 47.1 and 48.7 dB at 2.4, 5 and 6 GHz), minus 10 times the path-loss exponent times the logarithm of the distance, minus the loss of each wall on the way, minus a link margin of 8 dB for client antennas, body loss and fading. With 20 dBm EIRP on 5 GHz in a typical office (exponent 2.25), the signal stays above -65 dBm out to about 21.3 m in open space, and to about 21.3 m through one drywall wall.
How walls reduce signal
Typical planning values for one wall are shown below. Higher bands lose more, so Signal Plan multiplies the value you pick by 1.2 at 5 GHz and 1.35 at 6 GHz. Real values vary with thickness, reinforcement and furniture, so measure on site where it matters.
| Wall | 2.4 GHz | 5 GHz | 6 GHz |
|---|---|---|---|
| Glass | 2 dB | 2.4 dB | 2.7 dB |
| Drywall | 3 dB | 3.6 dB | 4.1 dB |
| Brick | 6 dB | 7.2 dB | 8.1 dB |
| Concrete | 10 dB | 12.0 dB | 13.5 dB |
| Lift or service core | 18 dB | 21.6 dB | 24.3 dB |
Measuring RSSI in practice
- Phone apps show RSSI from one radio and one antenna, so readings differ between devices by several dB. Compare readings taken with the same device.
- Take several readings per location and average them; the signal fluctuates by several dB even when nothing moves.
- For a design decision use an access-point-on-a-stick survey: mount a real access point at the planned position and measure around it.
Reading a heatmap
A heatmap colours each point by its strongest predicted signal. Use the legend to find your target level, and look at the outline that marks where the minimum RSSI is met. A secondary layer shows the second-strongest access point, which helps check roaming coverage, and a greyed overlay marks areas below the target.
Try it on your own floor plan with the free Signal Plan Wi-Fi heatmap planner. Methods and limits are explained on the methodology page.
Open the free Wi-Fi heatmap planner
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