WiFi Units Explained: Understanding mW, dBm, dB, and dBi

In our product descriptions, you will often come across abbreviations like dBi, dBm, mW, or Watts. What might seem like technical jargon at first glance is actually quite logical once you understand the principles behind it.

These units are the key to the performance of your WiFi equipment. Knowing these values ensures you buy the right accessories and get the most out of your hardware.

The golden rule: The higher the value (whether dBi, dBm, or mW), the stronger the transmit power or the gain of the component.

1. Milliwatts (mW) – Pure Transmit Power

Milliwatt (mW) is the unit for the actual physical power of your active WiFi devices – such as your router, access point, or USB adapter.

Since WiFi devices operate with very low energy, we use milliwatts instead of watts. In many regions, standard routers in the 2.4 GHz band typically operate with a legally limited power of 100 mW.

2. Decibels (dB) – The Practical Calculation Tool

Decibel (dB) is a logarithmic measurement. While it sounds complex, it is extremely practical for you: instead of multiplying with complicated formulas, you can simply add or subtract values in the networking world.

We use dB to describe the ratio of gain (amplification) or loss (attenuation). For instance, a long antenna cable might have a loss of 3 dB. To determine the total performance, you simply add up all the dB values of your components.

3. Decibel-Milliwatts (dBm) – Absolute Power

While dB only describes a ratio, dBm is an absolute power measurement referenced to 1 milliwatt. It is basically the power in Watts expressed in a more manageable, logarithmic way.

The typical 100 mW of a router corresponds exactly to 20 dBm. This scale is so useful because radio signals weaken extremely fast over distance.

4. Antenna Gain (dBi) – Focusing Power

dBi describes the gain of your antenna. Important to know: an antenna is a passive component. It does not create new power; it only focuses the existing energy more effectively.

• High dBi Value: Strong focus, high range, narrow beamwidth (ideal for point-to-point links).
• Low dBi Value: Wide coverage (omni-directional), shorter range (ideal for general room coverage).

🚨 Legal Warning: The EIRP Limit

The actual radiated power (EIRP) is strictly limited by law. It is calculated from the entire chain: Transmit Power (dBm) + Antenna Gain (dBi) - Cable Loss (dB).

Common Limits:

• 2.4 GHz Band: Maximum 20 dBm (100 mW).
• 5 GHz Band: Up to 23 dBm (200 mW) or even 30 dBm (1000 mW) allowed depending on the channel.