20 dBm Wi-Fi: How many meters will the signal last?

The question is how far the power will last 20 dBm, is one of the most common values ​​when designing a home network. Many users mistakenly assume that the number 20 means 20 meters or some other direct ratio, but the physics of radio waves is more complex. The actual range depends not only on the transmitter's output power but also on the receiver's sensitivity, the frequency range, and, of course, obstacles.

In open spaces, a signal of this strength can cover significant distances, tens or even hundreds of meters. However, in a city apartment or private home, the situation changes dramatically. Reinforced concrete walls, metal structures and even mirrors can absorb the lion's share of radio wave energy before it reaches your smartphone.

To understand the real picture of coverage, it is necessary to take into account that 20 dBm — is the equivalent of 100 milliwatts (mW). This is the standard, often maximum, power rating for many consumer routers in the 2.4 GHz band. Let's look at how this energy translates into meters of coverage under various operating conditions.

Converting dBm to milliwatts and its physical meaning

Before we talk about meters, it is important to understand what we are measuring. Decibel-milliwatt (dBm) — is a logarithmic unit of measurement of signal power relative to 1 milliwatt. The scale is logarithmic, meaning that a small change in dBm corresponds to a significant change in actual power in watts.

Meaning 20 dBm mathematically exactly corresponds 100 mWFor comparison, a typical router might have a power of 17 dBm (50 mW) or 23 dBm (200 mW). A difference of 3-6 dBm might seem insignificant, but in the world of radio signals, a 3 dBm increase in power doubles the signal energy, while a 3 dBm decrease cuts it in half.

However, even knowing the exact power in milliwatts, you can't simply take a ruler and measure the distance. Radio waves decay exponentially. If you double the distance from the source, the signal power will drop not by half, but by a factor of four (the inverse square law for free space).

Here's what the power ratio looks like to give you an idea of ​​scale:

• 📶 20 dBm — this is 100 mW, the standard maximum power for most civilian routers.
• 🔋 23 dBm — this is 200 mW, often found in powerful access points or routers with amplified antennas.
• 📉 17 dBm — this is 50 mW, a typical value for economical operating modes or older models.

⚠️ Note: Increasing transmitter power (for example, from 20 to 23 dBm) will not result in a proportional increase in range. You'll only see a small increase, which is easily offset by a thick wall.

Factors Affecting Signal Range

Why does one router with 20 dBm penetrate three rooms, while another "die" behind a single wall? The answer lies in a combination of factors, of which output power is only one parameter. Receiver sensitivity (your phone or laptop) is often a bigger bottleneck than the router's power.

The phone "hears" the router perfectly, but its own transmitter is too weak to "shout" back. As a result, you see full Wi-Fi coverage, but the internet doesn't work. This is a classic problem with an asymmetrical connection. Frequency is also critical: a 5 GHz signal attenuates much faster than a 2.4 GHz signal, even with the same power of 20 dBm.

Wall materials play a crucial role. Water contained in concrete, wood, and even living plants absorbs radio waves very well. Metal reinforcement in walls creates a Faraday cage effect, completely blocking the signal.

Main obstacles and their impact:

• 🧱 Load-bearing wall (concrete with reinforcement): weakens the signal by 15-25 dB (almost complete loss).
• 🚪 Wooden door or plasterboard: attenuation by 3-5 dB (the signal passes, but the speed drops).
• 🪟 Window glass (regular): attenuation of 2-4 dB, but tinting or metallized coating can remove the signal completely.

Also, don't forget about airwave noise. In an apartment building, your neighbors create background noise on the same frequencies. The router has to "shout" louder or wait for a pause in the airwaves, which reduces the effective range of a stable connection.

Signal range of 20 dBm in different conditions

Now let's get down to specific numbers. How many meters will 20 dBm penetrate? The answer depends heavily on your location. Under ideal laboratory conditions (open field, no interference), an access point with this power can provide a stable signal at a range of up to 100-150 meters.

In reality, everything is much more prosaic. Indoors, in conditions line of sight (For example, a long hallway in an office without partitions), a 20 dBm signal reliably maintains a level of -65...-70 dBm (good signal) at a distance of about 30-40 meters. This is sufficient for most apartments and small houses.

The situation changes when a wall gets in the way. A single 25 cm thick brick wall can absorb up to 15 dB of power. This means that your 20 dBm will be reduced to just 5 dBm (just over 3 mW) when it exits the wall. At this level, the signal will be extremely unstable even just 5-10 meters beyond the wall.

Approximate range values ​​for 20 dBm:

• 🏞️ Open space: up to 100 meters (for web surfing), up to 60 meters (for 4K video).
• 🏢 Office (open-space): 30-40 meters from the access point.
• 🏠 Apartment (through 1-2 walls): 10-15 meters of effective coverage.

⚠️ Note: The distances listed are for the 2.4 GHz band. In the 5 GHz band, the range will be approximately 1.5-2 times shorter under the same conditions.

It's important to understand that "range" is a flexible concept. A device may "see" a network from 50 meters away, but the connection speed will drop to a few kilobits per second, and the ping will rise to unacceptable levels.

The Impact of Wi-Fi Standards and Frequency Range

The 20 dBm power level manifests itself differently in different Wi-Fi standards. Older standards (802.11b/g/n) have a longer range but are slower. Newer standards (Wi-Fi 5, Wi-Fi 6, Wi-Fi 7) use complex modulations that require higher signal strengths (SNR) to operate at high speeds.

This means that a router with a power of 20 dBm, operating in the mode Wi-Fi 6 (802.11ax), can lose connection (high speed) much sooner than an old router loses any connection at all. Modern technologies sacrifice range for speed and spectrum efficiency.

The frequency range also dictates its own rules. The 2.4 GHz signal has a longer wavelength, allowing it to better bend around obstacles and penetrate walls. The 5 GHz signal (and especially the 6 GHz in Wi-Fi 6E/7) has a shorter wavelength and attenuates more quickly in materials.

Why does 5 GHz fade faster?

The physics behind the process are simple: the higher the frequency of a wave, the shorter its wavelength. Shorter waves bend less effectively around obstacles and are more readily absorbed by the atmosphere and wall materials. However, they carry more data per unit of time.

Therefore, if your goal is to cover a large area or a multi-story building, relying solely on 20 dBm in the 5 GHz band is pointless. Only a mesh system or repeaters will help.

Signal level calculation and attenuation table

For a better understanding of what's happening to your signal, it's helpful to refer to the attenuation table. Signal strength is measured in negative dBm (e.g., -50 dBm). The closer the value is to zero, the better the signal. -30 dBm is ideal (you're standing right next to the router), while -90 dBm is a complete loss of connection.

Below is a table showing how signal strength can change with distance from a 20 dBm source under typical conditions.

As the table shows, a single concrete wall reduces a powerful signal to a barely audible whisper. This is why, in large apartments, a single router is often insufficient, even if the specifications claim high signal strength.

Practical recommendations for improving coverage

If you realize that 20 dBm isn't enough for your space, don't rush to buy "amplifiers" of dubious quality. Often, the problem can be solved with proper setup and placement of the equipment. The first step should always be optimizing the router's location.

Place the device as high and centrally as possible in the apartment. Avoid placing it near microwaves, baby monitors, and large metal objects (refrigerators, cabinets). The router antennas should be oriented vertically for better horizontal signal propagation.

If optimization doesn't help, consider installing additional access points. Modern MESH systems They allow you to create a unified, seamless network where devices automatically switch between nodes. This is more effective than trying to "push through" a wall with the power of a single transmitter.

It's also worth checking the channel width settings. In the 2.4 GHz band, the channel width setting 20 MHz instead of 40 MHz may slightly increase range and stability at the expense of maximum theoretical speed, which is a worthwhile sacrifice in poor signal conditions.

⚠️ Caution: Using external high-gain (dBi) antennas changes the antenna pattern. A 5 dBi omnidirectional antenna "flattens" the signal, improving coverage broadly but degrading it up and down (on floors above and below).

Is it true that foil helps strengthen the signal?

Using foil or "cans" behind the router's antenna is a popular life hack. It works, but only in one direction. The foil reflects the signal, creating a directional beam. This can improve the signal in a specific room, but will completely "kill" it behind the router. Use this method only if you need to focus the signal on one specific point.

Can software power increase (200% in settings) harm the router?

Yes. Setting maximum power values ​​in the firmware (especially third-party firmware like OpenWrt or DD-WRT) can cause signal amplifiers to overheat. This reduces the device's lifespan and can cause unstable operation. 20 dBm is already high enough for home use.

Does the number of connected devices affect the signal range?

Physically, no; the transmitter power doesn't change. But logically, yes. The more devices there are, the more time the router spends polling each one. In weak signal conditions (-75 dBm and below), data packets are lost more often and require retransmission, which creates the illusion of slowness and a reduction in network range.

Is it worth buying a router with a declared power of 27 dBm?

For a typical home, that's unlikely. 27 dBm (500 mW) is already the level of professional equipment or outdoor access points. In an apartment, such a signal would create significant interference for your own devices and those of your neighbors, and could exceed health standards if left in close proximity for extended periods. Furthermore, your phone wouldn't be able to "respond" to the router with the same strength.

How to accurately measure signal strength in dBm on a phone?

In Android, this can be done through the engineering menu (code ##4636## in the dialer, then "Phone information") or special applications like WiFi AnalyzerOn iPhone, you need to hold down the Wi-Fi icon in the Control Center (on some versions of iOS) or use utilities like AirPort Utility with the scanner mode enabled in the settings.