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Understanding Wi-Fi Signal Strength (dBm)

If a number like "-65dBm" has ever left you wondering whether that is good or bad, here is how to read it.

What dBm actually is

dBm is a unit for absolute signal power, measured on a logarithmic scale referenced to 1 milliwatt (mW). Wi-Fi signal strength is almost always shown as a negative number, and the closer that number is to zero, the stronger the signal.

A rough signal strength scale

-30 to -50 dBm is generally excellent, -50 to -60 dBm is good, -60 to -70 dBm is fair (fine for browsing), -70 to -80 dBm is weak (may drop), and below -80 dBm is very weak and often unstable. Exact thresholds vary slightly by device and app.

How this relates to RSSI

RSSI (Received Signal Strength Indicator) is the underlying measurement of received signal strength; phones and apps often convert the same dBm value into a 0-100% bar display instead. Both numbers describe the same signal, just in different units.

Do not confuse dBm with dBi

dBm describes the signal power a device is actually receiving, while dBi describes antenna gain -- how much an antenna amplifies the signal it transmits or receives. A high-gain (high-dBi) antenna does not guarantee a strong measured dBm at your device, since distance and obstacles still apply.

How to check your own signal strength

On Windows, click the Wi-Fi icon in the taskbar and check the connection properties. On a Mac, hold Option and click the Wi-Fi icon in the menu bar to see the RSSI value in dBm directly. On a phone, a Wi-Fi analyzer app gives more detailed readings.

If your signal comes back weak

A low dBm reading usually comes down to distance from the router, obstacles like walls or appliances in the way, or channel congestion. From there, adjusting the router's placement or reducing interference is the practical next step.

Why the scale is negative and logarithmic

dBm measures power on a logarithmic scale, so small-looking number changes represent large real differences: roughly every 3 dB drop cuts the signal power in half, and every 10 dB drop cuts it to a tenth. That's why -70dBm is not just "a bit weaker" than -60dBm -- it's carrying only about a tenth of the power, which is why a signal can feel fine one room over and unusable two rooms further.

A device's own limitations matter as much as the signal

Two phones sitting in the exact same spot can report noticeably different dBm values, because antenna design and Wi-Fi chipset quality vary by device. A weak reading is not always a router problem -- it is worth testing more than one device before assuming the signal itself is the issue.

Frequently Asked Questions

Is -60dBm good or bad?

Generally, -60dBm is considered good -- solid enough for web browsing and video streaming without noticeable trouble.

Why do different devices in the same room show different dBm values?

Antenna quality and Wi-Fi chipsets vary by device, so even in the exact same location, the measured signal strength can differ somewhat from one device to the next.