Most people look at the typical ones mobile signal bars To know if you'll be able to make calls or browse the internet properly, but those bars are more misleading than they seem. Each manufacturer decides how much real signal corresponds to one, two, or five bars, so two phones in the same location can show different readings even if they're receiving almost the same signal strength.
If you really want to know how much coverage you have, both in mobile network as in WiFiYou need to learn how to read signal strength in dBm, understand what those negative numbers mean, how they relate to the bars, and what you can do when the values indicate a weak signal. Once you get the hang of it, it's much easier to diagnose connection problems and improve mobile coverage.
What is signal strength in dBm and why are bars so unreliable?
When your mobile phone or router connects to a wireless network, what they actually measure is the power of the radio signal they receive, expressed in dBm (decibels per milliwatt). This numerical value is what technicians and operators use to determine if a connection is good, bad, or simply unusable.
The coverage bars you see at the top are just one simplified graphical representation of that signal strength, but there is no standard that requires a manufacturer to use a specific dBm range for each bar. Therefore, one phone might show four bars while another, in the same location, shows three, even if the actual signal strength is similar.
On Android, iPhone, and most routers and WiFi access points, you can check the signal strength in dBm within status menus or testing tools. On many Android phones, you'll also see another number next to the dBm called ASU, which is an internal system way of expressing the same information in a more manageable way.
All of this applies to both the mobile coverage (2G, 3G, 4G, 5G) as with home or office WiFi: in both cases, signal strength is measured in dBm, almost always with negative values, and the closer they are to zero, the better the potential quality of the connection.
dB, dBm and ASU: differences without going crazy with the formulas
To fully understand what you're seeing on the diagnostic screens, it's worth distinguishing between dB, dBm and ASUBecause they're spelled similarly but they're not the same. You don't need to do math, but you do need to be clear about the measurements of each one.
The decibel (dB) is a logarithmic unit that compares two power levelsIt is used to indicate how much a signal has been amplified or attenuated; for example, a 3 dB increase implies approximately double the power, while a 10 dB increase represents a tenfold increase. It is a relative measure: it always refers to a change between two points.
The dBm (decibel-milliwatt) measures instead an absolute power level relative to 1 mWHere, nothing is being compared; it simply states the power of a specific signal. It's the standard scale in telecommunications for quantifying the signal strength received by a mobile phone, a 4G/5G router, or a Wi-Fi device.
Since the power reaching our devices is very low, that dBm scale is almost always used in negative valuesThis means that -50 dBm is a very strong signal, -80 dBm is reasonable, and -110 dBm is bordering on total loss of coverage; in this context, -60 dBm is better than -90 dBm, even though the number seems "smaller".
ASU (Arbitrary Strength Unit) is a internal signal strength unit which are primarily used by Android phones. The system converts dBm to ASU for more linear management, but the exact relationship depends on the network technology: GSM, UMTS, LTE, and NR (5G) use slightly different formulas. As a reference, for LTE, something similar to ASU ≈ dBm + 140 is typically applied within a certain range.
dBm ranges: from excellent signal to no coverage area
The dBm scale that you will see on both mobile and WiFi ranges, in practice, from close to 0 to values around -120 dBmwhere there is no longer a usable signal. As the number becomes more negative, the signal strength drops and it becomes more difficult to maintain a stable connection.
A commonly used guideline for assessing received signal strength, valid for both mobile and WiFi networks, would be something like this: starting from about -60 dBm means a very good signal, around -80 dBm of acceptable signal and below -100 dBm of quite weak signal, with risk of cuts and slowness.
Mobile networks typically use ranges like the following, based on the dBm values of the antenna reaching the phone:
- Starting from -120 dBm: no usable signal; the mobile usually displays “No service” (How to solve it).
- Between -120 and -104 dBmVery poor coverage, with serious problems establishing calls.
- Between -103 and -98 dBm: weak signal, very unstable calls and data.
- Between -97 and -90 dBm: average coverage, suitable for calls and basic browsing, but without much margin.
- Between -89 and -77 dBm: very good signal, clear calls and fast data.
- Between -76 and -60 dBmExcellent signal, with the possibility of almost fully utilizing the network.
Whereas in WiFi, the scale is usually expressed in RSSI (Received Signal Strength Indicator) and a typical range of 0 to -100 dBmIn this context, a signal between -30 and -50 dBm is excellent, between -51 and -60 dBm very good, from -61 to -70 dBm sufficient for most uses, and from -71 dBm onwards serious problems of speed and stability begin.
Another interesting fact is that some tools translate these values into quality percentages: in 2G/3G, for example, between -99 and -86 dBm can be considered 23-45% quality (delicate connection), between -85 and -72 dBm 45-67% (acceptable but sensitive to bad weather), and above -71 dBm a very high percentage, with stable connection and good data speed.
Types of mobile coverage and their typical speeds
Besides how much power reaches your device, the type of network technology whichever network you're connected to. Having a strong 2G signal is not the same as having a weak 4G or 5G signal, because the speed and latency capabilities vary considerably.
Among the standards that are still active or that you can find in the coverage icon are the following, with their indicative speeds under ideal conditions:
- G, GPRS or 2GDesigned for voice and SMS. Data speeds are around a few Kbps (about 6 Kbps), completely insufficient for current mobile internet usage.
- E, EDGE or 2.5G: an evolution of 2G that slightly improves data speeds, up to around 48 Kbps. It can be used for basic messaging, but little else.
- 3G (UMTS): first really useful standard for data, with rates that can range between 2 Mbps and 7,2 Mbps.
- H / H+ (HSDPA / HSDPA+): improvements over classic 3G, reaching up to 21 Mbps in laboratories and good conditions.
- LTE or 4G: the most widespread network in many countries; theoretically allows 100 Mbps or more, with real-world experiences varying greatly depending on the cell and congestion.
- 4G +: trade name for LTE with Carrier Aggregation, adding several bands at once; it can reach 300 Mbps and, in advanced deployments, approach Gbps.
- 5G: the most recent generation, with very high theoretical potential (several Gbps), although in day-to-day use it usually ranges between tens and hundreds of Mbps depending on the band, deployment and state of the network.
Combining network type and dBm level This is what truly determines your experience. -70 dBm on 4G or 5G is usually fantastic for almost any use, while the same figure on 2G is still poor for most current tasks.
To accurately characterize 4G and 5G coverage, more specific metrics are used, such as RSRP (Reference Signal Received Power) for data. This value, also in negative dBm, hovers around -80 dBm when the signal is very strong and drops to -100 dBm or less when the connection starts to weaken, especially inside buildings and in challenging environments.
How to view signal strength in dBm on Android
Android phones offer several ways to view the actual signal strength without just relying on the toolbars. Some depend on the manufacturer, but you almost always have at least one method without installing anything and several very useful apps to go further.
The most direct way, using system tools, usually involves going into the phone's status menu. The exact path varies, but it's typically something like "Settings → About phone → Status" or "Settings → About phone → Network/SIM status". There you should find a line called "Signal strength" with a value in dBm and sometimes another in ASU.
Android itself provides this information based on the mobile radio's parameters, and it's usually formatted like "-87 dBm 14 asu" or similar. The negative value is what you're interested in: the closer it is to zero, the better the coverage. The ASU figure is simply the same information expressed in other units that the system handles internally.
Some customization layers and even certain modified ROMs allow display the number directly in the status bar Instead of the bars, either as an official feature or with the help of specific apps, it's a very convenient way to monitor the signal without having to navigate through menus every few minutes.
If you want even more data, you can use apps like Signal Strength, Network Signal Info, Network Cell Info or CellularZ, which display the dBm in large letters, the type of network (2G, 3G, 4G, 5G), the frequency band and, in many cases, a map with the approximate position of the antenna you are connected to and the distance to it.
In some models it also works hidden test menu On Android: dial *#*#4636#*#* in the phone app and, if the manufacturer hasn't disabled it, a menu called "Tests" or "Phone Information" will open where you can see the signal strength, RSRP, RSSI, and other advanced parameters. Not all phones support it, but when it works, it's quite informative.
How to view signal strength in dBm on iPhone (Field Test Mode)
On iPhones, Apple doesn't display the dBm value directly in the status bar, but it includes a field test mode It's quite comprehensive with internal radio information. It's not very intuitive, but it works perfectly for checking signal strength.
Access is through the phone app. First, disable Wi-Fi to force the device to use only the mobile network (4G/5G). Then, open the phone app, dial *3001#12345#*, and tap "Call." A different interface will then open, called Field Test Mode.
Within these menus you will see sections related to LTE or NR (for 5G), such as “Serving Cell Meas”, “RsrpRsrqSinr” or “Cell Info”. In them you can locate the RSRP in dBm, which is the key reference signal strength value for data, along with RSRQ (quality) and SINR (signal-to-noise ratio), also very important for understanding the actual quality of the connection.
In older networks, such as 2G or 3G, parameters like RSSI or equivalent values, also in negative dBm, are commonly seen. Their interpretation is very similar: values close to -60 dBm are strong, while values approaching -100 dBm indicate that you are at the limits of coverage.
In older versions of iOS, it was possible to permanently replace the signal bars with the dBm reading, but that feature disappeared with more recent updates. Even so, test mode is still useful for accessing and checking the signal strength. actual signal strength in dBm, run coverage tests and return to normal use.
How to measure signal strength and the band used to install an amplifier
When you want to improve mobile coverage in a home, business, or rural area with a repeater, it is essential to know which frequency band is your carrier using at that point and exactly how much signal is reaching it. With a couple of steps you can get that data from Android or iPhone.
On Android, the most convenient option is to use a specialized app like CellularZ. After installing it from Google Play, it's advisable to disable Wi-Fi, enable mobile data (or voice only if you want to test GSM), and ensure that location services are turned on so the app can identify the cell tower.
When you open the application, choose the SIM slot you want to analyze (SLOT1 or SLOT2) and scroll down to the “Cell Params” section. There you will find an identifier of band like B1, B3, B7, B20etc., and also the uplink and downlink frequencies in MHz. In addition, the app will show you values such as RSRP (for 4G/5G) or RSSI/RxLev (for 2G/3G), all in dBm, which indicate the signal strength that an amplifier installed at that location would receive.
Without apps, on some Android devices you can use the testing menu: dial *#*#4636#*#*, go to "Phone information" for the desired SIM, and look for lines with "Signal strength," RSRP, or a number labeled E/U/ARFCN. This ARFCN or EARFCN value identifies the specific radio channelWith a frequency calculator like CellMapper, you can enter that number, choose the network type (2G, 3G, 4G, 5G), and get the exact band and frequency your phone is using.
On iPhone, the process is similar, but everything is done from Field Test Mode. After entering *3001#12345#* (after disabling Wi-Fi), you'll access sections like "Active Cell Information." There you'll see data called "Band Information" which indicates the LTE or NR band number; for example, a 3 would mean you're using the LTE band 3 (1800 MHz)Further down, in “Active cell measurements → RsrpRsrqSinr”, you will find the RSRP and RSSI values in dBm again.
With that information in hand, you can choose an amplifier that supports exactly the bands and frequencies used by your operator in your area, and get an idea of whether the signal coming from outside (for example, -100 dBm in a high band or -90 dBm in a low band) is sufficient as a basis for a kit with an outdoor antenna, amplifier and indoor antennas to work reliably.
WiFi signal in dBm, heat maps and factors that degrade it
In home and business Wi-Fi networks, signal strength is also measured in dBm, usually using a value called RSSI. Although many systems only display bars, it's possible to obtain exact figures from the system configuration or with specialized tools.
On Windows computers, for example, you can open a PowerShell or cmd window and use the command “netsh wlan show interfaces”. The displayed data includes a percentage of signal strength from the RSSI in dBm, along with information such as link speed, encryption type, and channel.
In general, a WiFi signal between -30 and -50 dBm indicates a outstanding coverageIdeal for very demanding tasks (online gaming, 4K video, many concurrent connections). Between -51 and -60 dBm you have a very good signal; from -61 to -70 dBm you will continue browsing without too many problems, although without maximum performance; below -71 dBm the connection becomes more fragile, and from -81 dBm onwards, continuous dropouts are normal.
To take it a step further, many businesses and advanced users create a "WiFi map" or heatmap of their home or office. With dedicated WiFi planning apps, you can upload a floor plan of the space, walk around with a laptop or tablet, and take RSSI measurements in dBm at various points. The result is a color-coded map that clearly displays the Wi-Fi signal. where there is good coverage and where you lack signal.
With these maps, you can decide whether to relocate your router, add repeaters or additional access points, or change channels to reduce interference. Tools like Acrylic WiFi Analyzer, NetSpot, and other analysis programs do precisely that: they measure signal strength, channel congestion, signal-to-noise ratio, and security level, and present everything in intuitive graphs.
Everything related to Wi-Fi is greatly affected by the router's position, distance, walls, floors, ceilings, appliances, and other nearby networks. A router in the most hidden corner of the house, right next to the microwave and close to the floor, can turn a connection of hundreds of megabytes into something that It behaves like a slow and unstable line.
Relationship between dBm, signal bars, and real-world experience
One of the things that confuses users the most is that sometimes the phone displays several bars but the connection is slow, or vice versa, you see few bars and yet everything is surprisingly smooth. This can be explained by combining what you know about the dBm ranges and network quality factors.
First, the signal strength indicator updates at its own pace and doesn't always accurately reflect the latest strength reading. The signal might suddenly drop, but the interface takes a few seconds to update, so for a while you'll still see a lot of bars when you're actually near the limit.
Secondly, the actual quality of the connection depends not only on the dBm, but also on the signal-to-noise ratio (SNR), cell or WiFi network congestion and the type of traffic. A -60 dBm signal in a saturated cell during peak hours can perform worse than -80 dBm in a lightly loaded cell at another time.
There are also occasional software issues: the system interface layer that displays the icons can freeze or fail to synchronize properly with the actual radio status. Some phones may show signal bars even when the problem lies with data access or authentication with the operator's network.
Therefore, when in doubt, the wisest thing to do is to look at the Signal strength in dBm and, if possible, do a speed test Or a simple call to check if the voice quality and latency match what the numbers indicate. It's much more reliable than relying solely on the bars.
How to improve mobile and WiFi coverage when dBm levels are low
If, after checking the values, you find you're below -95 dBm on mobile or -75 dBm on Wi-Fi, it's worth trying a range of practical solutions before moving on to more advanced equipment. Sometimes, a few simple changes are enough to gain several dB, as in our guide to 12 ways to increase cell signal.
When moving around, the first thing to do is move: going near a window, going up a floor, changing rooms, or even going outside can restore several signal points. Inside modern buildings, the walls and thermally treated windows can significantly reduce the signal strength coming from the nearest cell tower.
If you're at home, check where you've placed your router: ideally it should be in a central area. as central and elevated as possibleKeep your router away from appliances like microwaves, wireless base stations, and metal objects. A modern router compatible with WiFi 6 or 7, properly configured and with updated firmware, can also improve coverage and performance with the same internet provider.
Another interesting tactic is to separate devices by bands: take advantage of the 5 GHz band (or 6 GHz if you have WiFi 6E/7) for nearby devices that need high speed, and the 2,4 GHz band for more distant devices, which need more range even if they are somewhat slower.
Regarding the mobile phone, momentarily removing a very thick or metallic case can gain a small margin of signal, and it is advisable to check if the device is connected to the best available technology (4G or 5G) or is stuck on 3G or 2G due to a limited network setting (You can change your preferred network type) or an aggressive power-saving mode.
When none of these basic solutions are sufficient, especially in rural areas or buildings with very thick walls, the following come into play: mobile signal amplifiers or repeatersThese systems consist of an external antenna that captures the signal from the tower, an amplifier that boosts it, and one or more internal antennas that distribute it within the building.
A well-designed system can transform a signal approaching -100 dBm outdoors into much better values inside the home or office, with stable calls, fast mobile data, and less battery consumption on mobile phones because they no longer have to constantly transmit at their power limit.
However, in countries like Spain it is crucial that the repeater is compatible with the Operator bands and frequencies (B20, B3, B7, B1, B8 for 4G; n78, n28, n1, n3 for 5G, among others) and that it complies with European regulations on radio equipment (RED 2014/53/EU). Non-approved or improperly installed amplifiers can cause interference to mobile networks and result in penalties.
To refine your choice, it's a good idea to first measure which bands are actually used in your location with apps like CellularZ or Network Cell Info, and if necessary, consult with specialists to choose the right combination of outdoor antenna, cable length, and amplification power based on the dBm readings you get outdoors.
Understanding what signal strength in dBm is, knowing how to read the ranges from excellent coverage to the brink of disconnection, distinguishing between decorative bars and real numerical values, and knowing the technical factors that influence it (network type, frequency band, obstacles, noise, congestion) puts you in a much better position to diagnose why your mobile phone or WiFi isn't performing as it should and what specific steps you can take, from moving a few meters or relocating the router to considering a well-chosen amplification system adjusted to the reality of your environment.
