Most of us look at the typical mobile signal bars To know if we'll be able to make calls or browse the internet properly, but those icons are more misleading than they seem: they don't follow a standard, and each manufacturer interprets them in their own way. What really matters, and what technicians and operators use, is a negative number called dBm.
If you want to know precisely how much coverage you have, both in mobile network (2G, 3G, 4G, 5G) as well as WiFiYou need to learn how to read the signal in dBm, understand what those values mean, how they relate to the coverage bars, and what you can do when the numbers indicate that things are just barely adequate.
What is mobile signal strength in dBm and why are bars unreliable?
When your mobile phone connects to the network, what it's really measuring is the signal strength received from the antenna from your operator, expressed in dBm (decibel-milliwatt). That number is then translated into signal bars, but the conversion is not standardized.
There is no universal agreement that says that, for example, -85 dBm is equivalent to 3 bars Or that -100 dBm is 2 bars. Each brand and each customization layer decides its own ranges: two mobile phones next to each other, with the same SIM and in the same place, can show different bars even though the actual signal is almost identical.
Therefore, if you want a serious measure of coverage, you have to forget about bars for a while and focus on the Numerical reading of signal strength in dBmwhich is what truly reflects the quality of the connection reaching the phone or router and how improve mobile phone signal quality.
On Android and iPhone phones, and also on Wi-Fi routers, you can check these values directly. Sometimes, in addition to dBm, you'll see another figure called ASU, an internal unit that Android uses to manage signal strength more linearly.
dB, dBm and ASU: basic differences without getting confused
To understand what you're seeing on the screen, it's helpful to be clear about what the... dB, dBm and ASU valuebecause they are similar but not the same.
The decibel (dB) is a logarithmic unit that compares two powersIt is used to express how much a signal has been amplified or attenuated: for example, an increase of 3 dB roughly doubles the power, and a 10 dB increase multiplies it by ten. It is a relative measure, always comparing one level to another.
The dBm (decibel-milliwatt), on the other hand, is a absolute power measurement relative to 1 mWIt doesn't compare two signals, but rather tells you the power of a specific signal. It's the standard reference in telecommunications for quantifying mobile and Wi-Fi signal strength.
Since the power received by our devices is very low, the values are almost always expressed in negative dBmThe closer to 0, the better: -50 dBm is a very strong signal, -80 dBm is reasonable, -110 dBm is already on the verge of losing coverage.
ASU (Arbitrary Strength Unit) is an internal unit used primarily by Android mobiles to represent the signal intensity in a more linear wayASU is calculated from dBm, but the formula changes depending on the network type (GSM, UMTS, LTE, NR/5G). For example, in many LTE networks, an approximate value is ASU = dBm + 140, within a certain range.
dBm ranges: what is considered a good or bad signal
The dBm scale you'll see on your mobile phone, for both mobile and Wi-Fi networks, typically ranges from 0 to just under -120 dBm. Values above -60 dBm indicate a very strong signal, while below -100 dBm you start playing with fire.
As a practical reference, a commonly used scale for mobile and WiFi is this one, based on the received signal strength in dBm:
- Starting from -120 dBm: with no usable signal, the device usually displays “No service".
- Between -120 and -104 dBm: very low coverage, it's easy for a call to fail or the voice to cut out.
- Between -103 and -98 dBm: low coverage, data connection will be unstable and calls may be dropped.
- Between -97 and -90 dBmAverage coverage, sufficient for calls and basic browsing, but nothing special.
- Between -89 and -77 dBm: very good signal, clear calls and fairly fast data.
- Between -76 and -60 dBmExcellent signal, in theory you can take advantage of practically the maximum speed that the network offers.
These ranges are not set in stone, because they also have an influence. the type of network (2G, 3G, 4G, 5G), the frequency band, and congestionEven so, they serve as a quick guide to interpreting the number you see on the screen.
Important note: starting at around -100 dBm, the experience usually degrades considerably. You'll still be able to receive notifications and messages, but calls may sound tinny or drop out, and browsing becomes slow even if the phone still displays a bar.
Types of mobile coverage and approximate speeds
Besides the signal strength in dBm, the type of network you're hooked intoHaving an excellent signal on 2G is not the same as having -90 dBm on 4G or 5G.
These are the main types of coverage you can find in Spain and other countries, with their typical speeds under ideal conditions:
- G, GPRS or 2GVery old technology, designed for voice and SMS. Ridiculous data speeds, around 6 Kbps. It's hardly used for data these days.
- E, EDGE or 2.5G: an evolution of 2G that slightly improves speed, up to about 48 Kbps. It's suitable for very basic messaging and little else.
- 3G (UMTS)The first generation is truly useful for data. It allows browsing, email, and simple apps at speeds of around 2-7,2 Mbps depending on the implementation.
- H / H+ (HSDPA / HSDPA+): improvements over classic 3G, with rates that can reach 21 Mbps under good conditions.
- LTE or 4GThe dominant network in many places today. Theoretical speeds of up to 100-200 Mbps, and with Carrier Aggregation (4G+) speeds of around 1 Gbps can be reached.
- 4G +: Commercial name for 4G with multi-band aggregation. In practice, it allows speeds of 300 Mbps or more when the network and mobile device support it.
- 5GThe latest mobile generation. In the lab, it can reach up to 20 Gbps, but in reality, it depends heavily on deployment. In Spain, for example, a 5G NSA (supported by a 4G core) offers real-world speeds of around 100 to 800 Mbps, and a 5G SA can reach peaks of 1-2 Gbps or even more in favorable conditions.
Combining network type and dBm level This is what determines your experience: having -70 dBm on 4G or 5G is usually fantastic, while -70 dBm on 2G is still insufficient for almost everything we do today.
Mobile signal strength in dBm in 4G and 5G: what values are acceptable
In modern networks like 4G LTE and 5G, signal strength is expressed using specific metrics in addition to simple dBm. For data, the one you'll most often see in advanced menus is the RSRP (Reference Signal Received Power)which is still the power of certain cell reference signals, also in negative dBm.
In 4G/5G, an RSRP around -80 dBm usually indicates a Very good data coverageBetween -90 and -100 dBm, the connection starts to weaken, although browsing is still possible. Below -105 dBm, the connection may become unstable, especially indoors and with many people connected to the same antenna.
5G networks that use higher bands (such as 3,5 GHz or even mmWave in some countries) are more sensitive to obstacles, so to reach their full speed potential they need dBm values closest to 0 than the traditional low bands (700, 800 or 900 MHz).
In 2G and 3G, instead of RSRP, it is common to find RSSI or RxLev, also expressed in dBm. Their interpretation is similar: the smaller the negative value, the better, but the specific thresholds change slightly depending on the technology and the manufacturer.
Although each operator sets its own limits, as a rule of thumb you can consider that from about -95 dBm on mobile the experience starts to become questionable, especially if you need to stream video, play online games or upload large files.
WiFi in dBm: what you need for it to work smoothly
The WiFi coverage of your home, office or business is also measured in dBm, and is governed by the same principles as the mobile network: The closer the value is to 0, the better the signalHere, however, physical obstacles and interference from other networks have a much greater influence.
For WiFi, these intensity ranges are usually recommended for a comfortable experience:
- -30 to -50dBmVery strong signal, ideal if you're right next to the router. More than enough for any use, including high resolution and gaming.
- -51 to -60dBm: very good signal, perfect for HD/4K streaming, video calls and intensive use.
- -61 to -70dBm: acceptable, most tasks will go well, but there may be small drops in speed.
- -71 to -75dBm: reasonable limit, sufficient for browsing and using messaging apps, but far from maximum performance.
- Below -75 dBm: weak signal, you will notice interruptions, long loading times and problems with streaming or gaming.
Keep in mind that the band of 5 GHz (and 6 GHz in WiFi 6E/7) attenuates faster than that of 2,4 GHz. This means that a -70 dBm at 5 GHz can be more sensitive to walls and doors than the same value at 2,4 GHz, even though the maximum speed capacity is much higher.
In addition to the pure intensity in dBm, the following is key: signal-to-noise ratio (SNR)A strong but noisy signal can perform worse than a moderate signal in a clean environment. Many WiFi analysis apps display both data: dBm and SNR.
How to view signal strength in dBm on Android
Android offers several ways to check signal strength in dBm, both with the system as it comes from the factory and through specialized apps, which also add antenna information, maps and graphs.
The simplest method, without installing anything, is to go to phone status menuThe path varies depending on the brand and Android version, but it is usually similar to this:
- Settings → About phone → Status or SIM/Network status.
- Inside, look for an option called “Signal strength”, “Mobile network” or similar.
- You will see a negative number in dBm, and in many models also a value in ASU (for example, -87 dBm 14 asu).
Some custom ROMs or custom interfaces even allow the numerical value to be displayed in the status bar instead of the bars, either from the settings or through third-party tools.
If your phone doesn't easily display that data, you can use apps like Signal Strength, Network Signal Info, Network Cell Info or similar. These apps read the same signal strength values, but present them in a more user-friendly way: graphs, historical data, maps of nearby antennas, and, in some cases, a quality rating as POOR, FAIR, GOOD, or EXCELLENT based on dBm.
Another advanced option, which doesn't work on all devices because some manufacturers block it, is to use the internal test menu On Android: dial *#*#4636#*#* in the phone app, go to “Phone information” and check the “Signal strength” or RSRP/RSSI value shown for your SIM.
How to view signal strength in dBm on iPhone (Field Test)
On iPhones, Apple is more protective of network information, but there is still a internal test mode which allows you to see the dBm values and other advanced parameters of the cell you are connected to.
Access is done from the phone app itself, following these general steps:
- Turn off WiFi so that the phone uses only the mobile network (4G/5G).
- Open the calling app and dial * 3001 #12345 # *.
- Press the call button; the so-called Field Test Mode will open automatically.
In older versions of iOS, it was possible to make the signal strength bars permanently display a negative number, but this is no longer supported in more recent versions. Even so, sections like “LTE,” “Serving Cell Meas,” and “RsrpRsrqSinr” still appear in the test menu, where you'll see the RSRP in dBm for 4G/5G and other parameters such as quality (RSRQ) or signal-to-noise ratio (SINR).
For 2G and 3G, however, what you usually find is RSSI or similar values in dBm. The idea is the same: the higher the number (less negative), the better the actual coverage you have.
This test mode can vary considerably depending on the iOS version and carrier, and some models even display it differently. If you don't see clear RSRP or RSSI, try navigating through the LTE/NR menus until you find the Active Cell Measurements section.
Apps to measure mobile and WiFi signal in dBm
Beyond the system menus, there are many apps that translate the tangle of numbers on the network into information that is understandable and easy to compare between different sites, operators, or technologies.
Some of the most useful Android apps for mobile signal are Network Cell Info Lite, OpenSignal, CellularZ or Signal StrengthIts usual functions include:
- Display signal strength in dBm and ASU, for both mobile and WiFi.
- Please indicate what type of network you are connected to (2G, 3G, 4G, 5G) and what frequency band.
- Locate on a map the antenna or cell you are connected to, and show the approximate distance.
- Record signal history to see how it changes as you move.
In the WiFi realm, applications such as WiFi Analyzer, NetSpot or the Airport Utility itself in iOS (by enabling the WiFi scanner in settings) allows you to see the dBm of each nearby network, the channel, the band, the noise, and other details that help to Optimize the router's position and choose the best channel.
There are also more comprehensive tools, such as Speed Test Light, which in addition to download and upload speeds show latency, ping, jitter, and coverage mapsThese are not so much designed to read the exact dBm, but to check if, with the signal you have, the connection behaves as it should.
In almost all of these apps you will see the same logic repeated: classifying the signal into quality ranges (bad, regular, good, excellent) based on the dBm they measure, so you don't have to memorize all the thresholds.
Band, frequency, EARFCN/ARFCN and its relationship to dBm
When you get a little more technical, you'll see that many tools also indicate the frequency band and radio channel that you are using: B1, B3, B7, B20, n78, etc., or numbers like EARFCN/ARFCN.
LTE (4G) bands are labeled with numbers (1, 3, 7, 20, 28, etc.) that correspond to certain frequencies, for example: band 3 ≈ 1800 MHz, band 7 ≈ 2600 MHz, band 20 ≈ 800 MHz. In 5G, NR bands are identified with the prefix n (n1, n3, n28, n78, etc.).
The value E/U/ARFCN (Radio channel line) identifies a specific channel within those bands. With a tool like CellMapper's frequency calculator, you can enter the ARFCN or EARFCN and obtain the exact downlink band and frequency you are currently using.
Why does this matter for the dBm signal? Because the higher frequencies (above 1800 MHz) They suffer more losses and behave worse with walls, trees, and buildings; at the same dBm value, they can perform worse than the lower bands.
For comparative reference:
- -70 dBm: very strong signal in both low (700-900 MHz) and high (1800+ MHz) bands.
- -85 dBm: acceptable on low bands; may be somewhat lacking on high bands, especially indoors.
- -100 dBm: weak in high bands; in low bands it may still be usable, but with some instability.
This explains why sometimes, with the same dBm, the experience changes depending on the band your mobile is using: a low band penetrates walls better and maintains the call, while a high band can drop out with the slightest interference.
Factors that weaken coverage even if the dBm reading seems good
Understanding the dBm number you see on screen is only half the battle: the other half is the Factors that affect coverage and that can make your user experience not match what the phone seems to indicate.
The distance to the antenna is one of the key factors: the further away you are, the more the signal attenuates and The greater the negative value in dBm, the greater the negative value.Large rural areas or very deep inland areas tend to suffer particularly from this problem.
Physical obstacles are another major enemy: thick walls, concrete slabs, glass with reflective treatment (Low-E), metal structures, tall buildings nearby or even dense vegetation can reduce the power reaching the mobile phone by several dB.
In addition, there's interference from other devices and networks: microwaves, baby monitors, Bluetooth, other Wi-Fi networks on the same channel, etc. At 2,4 GHz, where Wi-Fi and many household appliances coexist, background noise can ruin a connection. theoretically good signal in dBm.
Finally, there's network congestion: in a packed stadium, at concerts, or during peak hours in busy areas, even if the dBm signal strength is decent, the cell can be saturated and simply unable to handle the load. You'll notice good coverage "in theory," but calls that don't connect and data speeds that are incredibly slow.
Why do you sometimes have signal bars but the actual coverage fails?
You've probably seen the battery bars almost full before, and yet your phone still won't make calls or charge anything. This kind of situation is usually due to a combination of factors. Delays in icon updates, software glitches, and network issues.
The signal strength icon doesn't always update at the same rate as the network. The signal might have dropped suddenly, but your phone hasn't refreshed the indicator yet. After a few seconds, the bars drop or the dreaded "No Service" message appears.
There are also scenarios where the signal arrives, but the network doesn't respond well due to antenna problems, operator maintenance, or configuration errors. In that case, the dBm is good, but the actual connection quality is poor.and you'll only notice it when you try to use the service.
On some Android devices, the problem might even lie in the launcher or the interface layer that renders the icons. If that component freezes, it can continue to display signal bars even when the radio is disconnected or in another state.
If in doubt, the most effective solution is usually to restart the phone, go to a more open area, or, in extreme cases, clear the cache of the system app that manages the interface (after making a backup) so that it synchronizes again with the actual network state.
Quick solutions when dBm indicates weak signal
If, when checking the dBm, you see figures below -95 dBm on mobile or -75 dBm on WiFi, it's advisable to take some basic steps to to shave off a few dB and improve the connection a little.
The simplest thing to do is move around: going to a window, going upstairs, changing rooms, or going outside can make a noticeable difference. Sometimes, just moving a few meters can improve the noise level by several decibels.
In the case of Wi-Fi, it's worth checking the router's location: place it in a central area of the home, elevated and away from microwaves, wireless base stations, and large metal objects. A modern router with Wi-Fi 6 or 7, properly configured and updated, can significantly improve both the dBm effective as connection stability.
With mobile phones, it's worth trying without a case, especially if you use metal or very thick cases. They won't reduce the signal by 20 dB, but they can slightly impact reception, and in areas with limited coverage, every dB counts.
Mobile signal boosters and repeaters: when do they make sense?
In homes, offices, or rural areas where the outdoor signal is already very weak (values close to or worse than -100 dBm), small improvements in position are not always enough. In these cases, a more robust option is to install a mobile signal amplifier or repeater.
These systems typically consist of three parts: an outdoor antenna, the amplifier itself, and one or more indoor antennas. The outdoor antenna is placed where the signal is strongest (roof, facade, mast), the amplifier boosts the signal, and the indoor antenna distributes it throughout the building.
With a properly sized repeater, you can go from almost nonexistent coverage to very reasonable dBm values throughout the interiorwith stable calls and much faster mobile data. In addition, the phone stops straining the transmission as much, which improves battery life.
In Spain and the European Union, it is essential that the equipment complies with the Radio Equipment Directive (RED 2014/53/EU) and is compatible with the bands used by operators (B20, B3, B7, B1, B8 in 4G; n78, n28, n1, n3 in 5G, among others)Using non-approved or improperly installed amplifiers can cause interference with the operator's network and result in penalties.
Before buying equipment, it's advisable to check with your mobile phone which bands and frequencies are being used at the installation point (using apps like CellularZ or Network Cell Info) and, if you have any doubts, consult specialists or the operator to ensure that the The repeater fits your specific case..
Mastering signal strength readings in dBm, understanding the meaning of intensity ranges, and how network technology, frequency bands, and the environment influence them allows you to stop blindly relying on coverage bars and start making informed decisions: from moving your router or changing rooms to choosing the best measurement app, locating the nearest antenna, or considering a certified amplifier when your home or business coverage falls short.
