WiFi Signal Strength details

WiFi Signal Strength details

WiFi signal strength is tricky WiFi Signal Strength details. The most accurate way to express it is with milliwatts (mW), but you end up with tons of decimal places due to WiFi’s super-low transmit power, making it difficult to read. For example, -40 dBm is 0.0001 mW, and the zeros just get more intense the more the signal strength drops.

RSSI (Received Signal Strength Indicator) is a common measurement, but most WiFi adapter vendors handle it differently, as it isn’t standardized. Some adapters use a scale of 0-60, and others 0-255.

WiFi Signal Strength details

WiFi Signal Strength details

Ultimately, the easiest and most consistent way to express signal strength is with dBm, which stands for decibels relative to a milliwatt. Since RSSI is handled differently by most WiFi adapters, it’s usually converted to dBm to make it consistent and human-readable.

  • mW – milliwatts (1 mW = 0 dBm)
  • RSSI – Received Signal Strength Indicator (usually 0-60 or 0-255)
  • dBm – Decibels in relation to a milliwatt (usually -30 to -100)

Reading dBm

The first thing to understand about dBm is that we’re working in negatives. -30 is a higher signal than -80, because -80 is a much lower number.

Next, it’s important to know that dBm does not scale in a linear fashion like you’d expect, instead being logarithmic. That means that signal strength changes aren’t smooth and gradual. The Rule of 3s and 10s highlights the logarithmic nature of dBm:

3 dB of loss = -3 dB = halves signal strength
3 dB of gain = +3 dB = doubles signal strength
10 dB of loss = -10 dB = 10 times less signal strength (0.1 mW = -10 dBm, 0.01 mW = -20 dBm, etc.)
10 dB of gain = +10 dB = 10 times more signal strength (0.00001 mW = -50 dBm, 0.0001 mW = -40 dBm, etc.)