Those little bars on your phone screen are lying to you. While they might show full signal strength, your calls still drop and your data crawls at a snail's pace. The problem is that signal bars provide a vague approximation that varies wildly between phone models and carriers, giving you no real insight into your actual cell signal strength.
Professional technicians never rely on these misleading bars when they need to test cell signal accurately. Instead, they use precise dBm (decibel-milliwatts) readings that reveal your true connection quality. This measurement typically ranges from -50 dBm (excellent) to -120 dBm (very poor), with signal strength doubling every three decibels. A reading of -97 dBm is actually twice as powerful as -100 dBm.
Fortunately, your smartphone already has a hidden field test mode built right into it. We'll show you how to access this professional tool and perform the same cell signal strength test that experts use to get precise measurements. With this knowledge, you'll finally understand what's really happening with your connection and can take action to fix any problems.
Why Signal Bars Are Not Reliable
Signal bars are fundamentally flawed indicators that mislead users about their actual connection quality. While most people trust these bars to show signal strength, they provide surprisingly unreliable information that can lead to poor decisions about your cellular service.
How different phones interpret bars
Each phone manufacturer-Apple, Samsung, Google, and others-uses their own proprietary algorithms to display signal bars. This means one phone's two-bar signal might measure -88 dBm while another phone's two-bar signal registers at -70 dBm (remember, closer to 0 is stronger).
This creates a major problem when trying to compare signal strength between devices. Two people standing in exactly the same spot with different phone models might see completely different bar readings. You could have two bars and stream video without issues, while your friend shows four bars yet can't send a text message.
Even worse, some phone models don't update the bar display for up to 15 minutes, so what you're seeing might not reflect your current signal reality. Each manufacturer interprets and displays signal strength according to their own criteria, making bars essentially meaningless for accurate testing.
Why bars don't reflect real signal strength
Signal bars only show relative strength without telling you the actual measurable dBm value. They also don't distinguish between signal strength (RSRP) and signal quality (RSRQ), both of which affect your connection experience.
You might have full bars but still experience poor performance due to:
- Network congestion from too many users sharing limited bandwidth
- Signal interference from buildings, weather, or electronic devices
- Poor signal quality despite strong signal strength
- Tower distance and antenna orientation issues
It's not unusual for a one-bar signal in one location to outperform five bars in another location. This happens because signal strength is just one factor determining cellular performance. What matters most is data speed, reliability, and consistency-none of which can be represented by simple bars.
Additionally, bars might not clarify whether they're showing your voice connection or data connection. You could have excellent voice call quality but terrible data speeds, or vice versa, with no way to tell the difference from the bars alone.
Professional technicians understand these limitations, which is why they never rely on bars when conducting a proper cell signal strength test. The only reliable way to measure your true connection is through precise dBm readings.
Many users report having full bars but connections that are "slow as dirt". This happens because bars don't account for critical factors like network capacity and the number of users currently connected to the same tower.
Getting accurate signal measurements requires looking beyond these oversimplified indicators to understand what's really happening with your connection.
Understanding dBm and RSRP
Now that you understand why signal bars are unreliable, let's examine the precise measurements that professionals use when they conduct a cell signal test. These two critical metrics-dBm and RSRP-provide the accurate information you need to understand your true connection quality.
What is dBm and how it works
dBm stands for decibel-milliwatts, the gold standard for measuring cell signal strength. This unit expresses the power level of your cellular connection as a negative number, typically ranging from -50 dBm (excellent) to -120 dBm (very poor). Fundamentally, dBm measures how much power reaches your device from the cell tower.
The dBm scale is logarithmic, which creates an interesting effect: signal strength doubles every three decibels. For instance, a -90 dBm signal is twice as powerful as a -93 dBm signal. Similarly, a -84 dBm reading indicates four times more signal power than -90 dBm. This explains why seemingly small numerical improvements can dramatically enhance your connection quality.
When conducting a cell signal strength test, remember this rule: the closer the dBm value is to zero, the stronger your connection. Generally, readings stronger than -85 dBm indicate usable, strong signals. Here's how to interpret your readings:
- -50 to -70 dBm: Excellent signal (nearly perfect)
- -71 to -85 dBm: Good signal (reliable performance)
- -86 to -100 dBm: Fair signal (occasional issues)
- -101 to -110 dBm: Poor signal (frequent problems)
- Below -110 dBm: Very poor signal (barely usable)
Difference between dBm and dB
Professionals often use both dBm and dB terms, yet they measure entirely different things. The decibel (dB) is a dimensionless unit that quantifies the ratio between two values-essentially measuring relative change. Meanwhile, dBm expresses absolute power level referenced to one milliwatt.
To illustrate this distinction: if your outdoor signal measures -90 dBm and you install a signal booster rated at 70 dB gain, your indoor signal would improve to approximately -20 dBm. Here, dBm represents the actual signal strength at specific locations, whereas dB indicates how much the signal amplifies between those points.
A simple rule to remember: use dB when expressing the ratio between two values (gain or loss) and dBm when determining exact power levels. Unlike the misleading signal bars, these measurements provide consistent, standardized readings across all devices and carriers.
What is RSRP and why it matters
Reference Signal Received Power (RSRP) represents the next evolution in signal measurement, particularly for 4G LTE and 5G networks. RSRP specifically measures the power of reference signals spread over the full bandwidth. Unlike general signal strength readings, RSRP focuses exclusively on the reference signals that maintain your connection to the tower.
RSRP values typically range from -140 dBm (very weak) to -44 dBm (very strong), with usable signals usually falling between -75 dBm (close to a tower) and -120 dBm (at coverage edge). RSRP excels at measuring signal power from a specific sector while potentially excluding noise and interference from other sectors.
What makes RSRP vital for accurate signal testing? Unlike older metrics, RSRP provides a clearer picture of your actual connection quality to a specific tower. This precision helps network operators identify weak coverage areas and optimize their infrastructure. For you as a user, understanding RSRP helps diagnose whether your connection issues stem from weak signal strength or other factors like interference.
RSRP works alongside RSRQ (Reference Signal Received Quality), which measures signal quality rather than just strength. Together, these metrics provide comprehensive insight into your connection that signal bars could never deliver. A strong RSRP reading typically translates to faster data speeds, better call quality, and more reliable overall performance.
How to Check Cell Signal Strength on Android
Android phones give you several ways to check your actual signal strength without relying on those misleading bars. These methods provide the precise dBm readings you need for an accurate cell signal test.
Using Field Test Mode on Android
Field Test Mode varies depending on your Android device and operating system version. Make sure to turn off your WiFi connection before testing. Here are the most common ways to access it:
Method 1 (Most Common):
- Go to Settings
- Tap About Phone
- Tap Status or Network
- Tap SIM Status
- Look for Signal Strength
Method 2:
- Go to Settings
- Tap More Options or More Settings
- Tap About Phone
- Tap Mobile Networks
- Find Signal Strength
Method 3 (Direct Code):
- Open your Phone app
- Dial ##4636##
- Tap Phone Information
- Find Signal Strength in dBm
Some manufacturers use specific codes: Samsung (#0011#), HTC (##7262626##), and Sony (##386##).
Best Android apps for signal testing
If the built-in methods don't work on your device, these apps can perform a thorough cell phone signal test:
Network Cell Info Lite: Shows real-time cellular signal monitoring with color-coded displays for signal strength, frequency bands, and signal quality. Many professionals consider this the best cell signal tester available.
weBoost App: Designed specifically to simplify signal testing and instantly measures dBm for Android phones. You don't need to own a weBoost product to use it.
SignalStream: Allows you to save and share 3G, 4G, and 5G signal readings. This is particularly useful for getting expert recommendations based on your specific readings.
LTE Discovery: Analyzes LTE, 4G, and 5G signals while automatically displaying signal strength and even identifying the direction of the cell tower you're connected to.
Tips for accurate Android signal readings
To get reliable results from your cell signal strength test:
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Android phones read only one network at a time. If you have 4G access, that's the default dBm reading displayed.
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Take multiple readings in different locations throughout your property. Signal strength updates every few seconds as you move.
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Test signal at various times of day since network congestion and usage patterns change.
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Remember that signal strength doubles every three dBm closer to zero. A reading of -87 dBm is twice as strong as -90 dBm.
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For complete testing, measure signal on each side of your building (north, south, east, west), upstairs areas if you have them, and rooms where you use your phone most.
Android's flexibility makes it much easier to test cell signal compared to iPhones, giving you both built-in tools and powerful third-party options.
How to Check Cell Signal Strength on iPhone
Testing signal strength on iPhones is more complicated than Android devices because Apple keeps changing how their Field Test Mode works. Unlike Android phones that offer multiple testing methods, iPhones rely primarily on a hidden Field Test Mode that Apple frequently modifies with each iOS update.
Accessing Field Test Mode on iPhone
To reveal your iPhone's true signal strength:
- Turn off your WiFi connection to ensure you're measuring cellular signal only
- Open the Phone app and dial 3001#12345# then press call
- The Field Test menu will appear, giving you access to detailed signal information
- Look for "RSRP" numbers which show your actual signal strength
Remember that readings closer to zero indicate stronger connections. A signal of -60 dBm is much stronger than -80 dBm, with every 3 dBm improvement effectively doubling your signal power.
iOS version differences and limitations
Unfortunately, Apple frequently changes Field Test Mode with iOS updates, which creates problems for people trying to test their signal. Each iOS version displays information differently:
- iOS 16: Depending on your iPhone model, either tap "RsrpRsrqSinr" or "Reach Attempt under LTE" to find signal strength
- iOS 15: Look for RSRP on the dashboard or tap Menu → Cell Info under RAT
- iOS 14 & 13: Tap Menu → Serving Cell Meas to find RSRP values
- iOS 12 & 11: Process differs between Intel and Qualcomm chipsets
Not every iPhone can display dBm readings-it depends on your device's carrier and chipset. Recent iOS updates (especially iOS 17+) have made it even harder to access detailed signal information.
Using speed test apps as alternatives
When Field Test Mode doesn't work on your iPhone, these apps can help:
- OpenSignal: Provides speed tests for 4G/LTE, 5G, and WiFi plus coverage maps to identify your carrier's coverage quality
- Speed Test by Ookla: Quickly measures download and upload speeds with a single tap
- weBoost app: Guides you through the field test mode process even if it doesn't calculate dBm directly
While speed test results aren't as precise as dBm readings, they give you more reliable information than simply counting signal bars.
What Your Signal Strength Means
Once you've gotten your precise dBm measurements, you need to know what those numbers actually tell you about your connection. The raw readings reveal much more than just whether you can make a call or send a text.
Signal strength ranges explained
Signal strength measured in dBm typically falls within these ranges:
- -50 to -79 dBm: Excellent - Crystal clear calls and lightning-fast data
- -80 to -89 dBm: Good - Reliable service with steady data speeds
- -90 to -99 dBm: Fair - Slower data but acceptable call quality
- -100 to -109 dBm: Weak - Expect dropped calls and buffering
- -110 to -120 dBm: Poor - Spotty to no service
Remember that the dBm scale is logarithmic, not linear. Each 3 dBm improvement doubles your signal power. For instance, improving from -100 dBm to -97 dBm doubles your signal strength.
How signal quality affects performance
Signal strength is only part of the equation. Signal quality refers to how clean and usable your connection is. Even with strong signal strength, poor quality can result in slow speeds and frequent disconnections.
Signal quality is measured using:
- SINR/SNR (Signal-to-Interference-plus-Noise Ratio): Higher values mean clearer connections. Above 10 dB is excellent, 5-10 dB is good, while 0 dB is merely acceptable
- RSRQ (Reference Signal Received Quality): Ranges from -19.5 dB (poor) to -3 dB (excellent)
Signal quality represents how much interference exists between your device and the tower. Less noise allows for clearer calls and faster data speeds.
Why good dBm doesn't always mean good service
Having strong signal strength (-70 dBm) doesn't guarantee good performance. Several factors can impact your actual experience:
- Network congestion: Too many users on a single tower
- Tower capacity: When towers exceed capacity, service deteriorates regardless of signal strength
- Interference: Buildings, weather, electronic devices, and other signals can degrade quality
- Frequency bands: Different bands offer various combinations of speed and coverage
Both signal strength and quality must be evaluated together to understand performance. You might have excellent dBm readings but still experience slow data due to tower load or interference.
Conclusion
Signal bars have been misleading you about your true connection quality, but now you have the tools to get accurate measurements. With field test mode on your phone, you can access the same precise dBm readings that professional technicians use to diagnose connection problems.
You now know how to test your cell signal strength properly, whether you have an Android or iPhone. More importantly, you understand what those dBm numbers actually mean for your calling and data experience. Strong signal strength doesn't always guarantee good service, but it gives you a starting point for troubleshooting your connection issues.
With this knowledge, you can make informed decisions about your wireless service. You can identify dead zones in your home or office, compare carrier performance in your area, and determine whether a signal booster might help improve your connection.
If you have any questions about testing your cell signal strength or need help interpreting your readings, please call us at 800-590-3564 and we'll be happy to help you solve your connection problems.
Key Takeaways
Understanding your true cell signal strength requires looking beyond misleading signal bars to access professional-grade measurements that reveal your actual connection quality.
• Signal bars are unreliable - each phone manufacturer uses different algorithms, making bars inconsistent across devices and carriers.
• Use Field Test Mode to access real dBm readings - dial ##4636## on Android or 3001#12345# on iPhone for precise measurements.
• Signal strength ranges from -50 dBm (excellent) to -120 dBm (poor) - every 3 dBm improvement doubles your signal power.
• Strong signal doesn't guarantee good service - network congestion, tower capacity, and interference affect performance regardless of dBm readings.
• Test multiple locations and times - signal strength varies throughout your property and changes based on network usage patterns.
Professional technicians never rely on signal bars because they understand that accurate troubleshooting requires precise dBm measurements. With these hidden phone methods, you can now diagnose connection issues, compare carrier performance, and make informed decisions about signal boosters using the same tools experts use.