Updated: April 14, 2026 | Reading time: approx. 6 minutes | Your expert guide to network technology
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. Whether you want to set up a point-to-point bridge or just improve the signal in your living room: 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.
| Power in mW | Equivalent in Watts |
|---|---|
| 1 mW | 0.001 Watts |
| 100 mW | 0.1 Watts |
| 1000 mW | 1 Watt (allowed in some 5 GHz bands) |
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 of your system, you simply add up all the dB values of your components (cables, connectors, surge protectors).
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. dBm makes these massive differences in power easier to represent.
| dBm Value | Power in mW |
|---|---|
| 0 dBm | 1 mW |
| 17 dBm | 50 mW |
| 20 dBm | 100 mW |
| 30 dBm | 1000 mW (1 Watt) |
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.
Imagine a light bulb (0 dBi) shining in all directions. An antenna with a high dBi value is like a flashlight: it focuses the light into a strong beam. It shines much further, but in a narrower area.
- 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.
Calculation Example: If your router transmits at 15 dBm and you connect a 9 dBi antenna directly without a cable, you end up with 24 dBm. In the 2.4 GHz band, this would already be illegal! Always ensure the right combination of router power and antenna gain.
Conclusion: Knowledge Prevents Bad Purchases
Now you understand that dBi doesn't refer to the "power" of the router, but how much an antenna focuses the signal. With this knowledge, you can optimize your WiFi system, solve range issues, and always stay within the legal limits.
FAQ: Common Questions About WiFi Units
Is a higher dBi antenna always better?
Not necessarily. A 12 dBi antenna has a very narrow beam. For a house with multiple floors, a 5 dBi antenna is often better as it distributes the signal more broadly, providing better overall coverage.
What does a negative dBm value mean in my WiFi analysis?
Reception strength (RSSI) is almost always shown as a negative value. The closer the value is to zero, the stronger the signal. -30 dBm is excellent, while at -80 dBm, the connection becomes unstable and usually drops.
How are dBm and mW related?
They are two different ways of describing the same power. mW is linear, dBm is logarithmic. An increase of 3 dBm always means doubling the power in mW (e.g., from 50 mW / 17 dBm to 100 mW / 20 dBm).
Why is cable loss in dB so important?
Every cable and connector absorbs signal energy. If you buy a strong antenna but use 10 meters of low-quality cable, the antenna's gain can be completely negated by the cable loss (attenuation).