When you see a Wi-Fi icon with a full or partial set of bars on your smartphone or laptop screen, you're likely wondering about the connection quality. However, these graphical indicators often mask the true picture of what's happening on the air. For in-depth network diagnostics and equipment configuration, it's important to understand What exactly is Wi-Fi signal strength measured in? and how to interpret the obtained values.
The basic unit of measurement of the received signal level is dBm β decibel-milliwatt. This is a logarithmic value that shows the ratio of signal strength to a reference value of one milliwatt. This is the parameter displayed by professional broadcast scanning utilities, and it is the one to rely on when searching for "dead zones" in an apartment.
In addition to reception power, there is a concept antenna gain, which is measured in dBiMany users confuse these values, believing that the higher the number on the router's box, the better it will penetrate walls. In fact, dBi characterizes the antenna's ability to focus radiation in a specific direction, rather than generating energy out of nowhere. The differences between these parameters are critical for selecting the right equipment.
Basic unit of measurement: Decibel-milliwatt (dBm)
In the world of wireless technologies, the de facto standard for expressing signal strength has become the value dBmIt's convenient because it allows you to work with compact numbers instead of microscopic watt values. A Wi-Fi signal attenuates as it travels through space, and its power drops by orders of magnitude, so a logarithmic scale is indispensable here. It's important to remember one key rule: dBm values ββare always negative (except when you're in close proximity to the transmitter, which is rare).
The closer the value is to zero, the stronger the signal. For example, a level of -40 dBm is significantly more powerful and better quality than -80 dBm. A difference of 3 dBm means a twofold change in power, and a difference of 10 dBm means a tenfold change. Therefore, a drop in signal from -60 to -70 dBm isn't just "getting a little worse," it's tenfold reduction in power received radiation.
Understanding the dBm scale helps avoid misconceptions. If your router displays a transmit power of 20 dBm, this doesn't mean you'll get the same 20 dBm at the receiver. The signal dissipates, is absorbed by walls, and is reflected. At a distance of several meters in an open room, you can already see values ββaround -45...-55 dBm. Behind a single brick wall, the signal can drop to -70 dBm, which is already the limit for stable operation.
Antenna Gain: Myths About the Decibel-Isotropic Rating (dBi)
You'll often see "Gain 5 dBi" or "9 dBi" on router boxes or individual antennas. Many people mistakenly interpret this as the router's own power, but dBi β is a unit of measurement of antenna gain relative to an isotropic radiator. An isotropic radiator is a theoretical antenna that radiates a signal uniformly in all directions, forming a perfect sphere.
A real antenna can't create energy; it can only redistribute existing energy. By increasing the gain (dBi), we "flatten" the radiation pattern. Imagine a balloon: if you press on it from above and below, it expands laterally. Similarly, a high-gain antenna "picks up" the signal from above and below, directing it horizontally. This is useful for covering large areas on a single floor, but can degrade the signal on floors above or below.
- π‘ Low gain (2-4 dBi): The signal spreads more spherically, better covering multi-story buildings, but has a shorter range at one point.
- π― High gain (9-12 dBi): The signal βbreaks throughβ further in a straight line, but has a narrow beam, which requires precise orientation of the antenna.
- βοΈ Balance: For a standard apartment, antennas with a gain of 5 dBi are usually optimal, providing a balance between coverage and range.
Why can't you just install a 20 dBi antenna?
An antenna with 20 dBi gain will turn the antenna pattern into a thin "pancake." The signal will travel very far horizontally, but the coverage area immediately above and below the router will disappear. Furthermore, such antennas are often large and require precise polarization adjustment.
Linear Power: Milliwatts (mW)
In the technical specifications of transmitters and in the settings of some routers (especially in the section on adjusting the transmission power), you can find a linear unit of measurement - milliwatts (mW or mW)Unlike the logarithmic dBm scale, the relationship here is direct: 100 mW is twice as powerful as 50 mW. However, due to the vast range of values ββ(from thousandths of a watt to hundreds of milliwatts), engineers find it more convenient to use dBm.
Conversion between these values ββis done using a formula, but for everyday use, knowing a few key correspondences is sufficient. The maximum permitted power of Wi-Fi transmitters is strictly regulated in most countries to prevent interference with other devices and harm to health. It typically does not exceed 100 mW (20 dBm) for the 2.4 GHz band.
β οΈ Attention: Don't attempt to artificially increase the transmit power in your router settings above the default values ββ(if this option is hidden in the firmware). This may lead to overheating of the Wi-Fi module, nonlinear signal distortion, and interference with neighboring networks, which will ultimately reduce overall network speed.
It is important to understand the difference between power transmissions (Tx Power) and sensitivity reception (Rx Sensitivity). The router can "shout" very loudly (high power in milliwatts), but if your smartphone has a weak receiver, it won't "hear" the router's response. Communication is a dialogue, and it only works when both parties can hear each other.
Unit Conversion: Conversion Table
To help you understand the relationship between logarithmic and linear values, as well as to assess signal quality, we've provided a summary table. It will help you quickly navigate any confusing numbers in the diagnostic utility.
| Signal level (dBm) | Power (mW) | Connection quality | Description of the condition |
|---|---|---|---|
| -30... -45 | 0.03 - 0.001 | Ideal | Be in the same room as the router |
| -50... -60 | 0.0001 - 0.00001 | Excellent | Stable performance, 4K video, and gaming |
| -65... -70 | ~0.000003 | Good | Normal operation, occasional drops are possible |
| -75... -80 | ~0.0000001 | Bad | Web surfing is possible, video buffering |
| -85... -90 | ~0.00000001 | Critical | There is a connection, but it gets lost and accessing the network is difficult. |
SNR: Signal-to-noise ratio as a quality criterion
Signal strength alone (even if it is measured in dBm and appears high) does not guarantee high speed. The key parameter is SNR (Signal-to-Noise Ratio) β signal-to-noise ratio. Noise is background radiation from microwaves, Bluetooth headsets, neighbors' routers, and household appliances. If your signal is -60 dBm, but the noise level is -62 dBm, then useful information is drowned out by interference.
SNR is also measured in decibels (dB), but unlike signal strength, it's a positive number. The higher the number, the better. The formula is simple: SNR = Signal Level - Noise LevelFor example, with a signal of -50 dBm and noise of -90 dBm, the ratio will be 40 dB. This is an excellent result. However, if the signal is -70 dBm and the noise is -75 dBm, the SNR will be only 5 dB, and the connection will be extremely unstable.
- π SNR less than 10 dB: Communication is almost impossible, there are constant breaks.
- β οΈ SNR 10-20 dB: Low speed, packet loss possible.
- β SNR 25 dB and above: Comfortable work, high data transfer speeds.
β οΈ Attention: The noise level in the air is variable. A neighbor might turn on the microwave at 7:00 PM, and your SNR will drop sharply, even though your router's signal strength remains the same. Therefore, it's best to conduct measurements at different times of day.
Practical measurement and signal analysis
To translate theoretical knowledge into practice, you need to take measurements in your room. Operating systems display this information differently. In Windows, the standard interface only displays "bars," which are subjective. For accurate dBm data, it's best to use specialized software.
On Android smartphones, you can use the built-in engineering menu or third-party analyzer apps. On iOS, options are limited due to Apple's security policies, but apps from router manufacturers are suitable for an initial assessment. On a Windows PC, an excellent tool is the utility inSSIDer or console command.
To get basic information in Windows, you can use the built-in command line. Open the terminal (cmd) and enter the following command:
netsh wlan show interfacesIn the output, find the "Signal" line; it will be displayed as a percentage. To see the exact value in dBm, you'll need more advanced utilities, such as Wi-Fi Analyzer or Acrylic Wi-Fi HomeThey will plot a graph where the Y-axis is power in dBm and the X-axis is time or channels.
βοΈ Checking the quality of your Wi-Fi network
Factors Affecting Signal Attenuation
Knowing how power is measured, it's important to understand why it drops. Radio waves lose energy when passing through obstacles. Different materials absorb signals at different rates. For example, open space introduces virtually no loss other than natural scattering.
Drywall walls attenuate the signal only slightly (2-4 dB), while brickwork can reduce it by up to 10-15 dB. Reinforced concrete floors and metal doors are a virtually impenetrable barrier, introducing attenuation of 20-30 dB or more. Mirrors and tinted glass also act as a screen, reflecting the signal.
It is also worth considering the influence of the range. Signal frequency 5 GHz has a shorter wavelength than 2.4 GHzThis allows for more data transfer, but it's less effective at avoiding obstacles and attenuates faster in walls. Therefore, in a far room, you might see -75 dBm on 5 GHz, while on 2.4 GHz you'll see a solid -60 dBm.
How to improve signal if the power is low?
If measurements show values ββworse than -75 dBm in work areas, consider the following options: moving the router to the center of the apartment (or higher), replacing antennas with more directional ones (with higher dBi), switching to a Mesh system for seamless coverage, or using Powerline adapters that transmit the Internet through electrical wiring.
Does the number of connected devices affect signal strength?
No, the number of devices doesn't affect the physical transmit power (dBm). However, it does affect channel throughput and response time. The router divides the airtime between clients. If there are many devices, each one gets less time to transmit data, which subjectively feels like a "weak internet connection," even though the signal strength (RSSI) remains the same.
Is it true that foil on an antenna strengthens the signal?
The foil acts as a reflector, changing the radiation pattern. It can boost the signal in one direction (by reflecting it off the wall), but it's guaranteed to weaken it in the opposite direction. This is a crude method that produces unpredictable results and often creates interference. It's better to use standard antennas with the correct gain.