What is dBm and How Does it Affect Your Cell Signal?

What is dBm and How Does it Affect Your Cell Signal?

Written by Wilson Amplifiers
5th Aug 2019

The Surprising Truth About Cell Phone Bars and dBm

Ever wondered how to get the most accurate measurement of your cell phone's signal strength?

You're probably thinking, “Signal bars, duh.” Well, that's not entirely correct.

Those coveted signal bars we're constantly bending, twisting, and stretching to gain better access to? They're purely aesthetic.

Don't get us wrong, signal bars can provide a general idea of how strong your signal is at any given location. However, they lack a universal standard. The number of bars you see all depends on the algorithm your carrier or phone uses to represent signal strength as cell phone bars. So, while the friend sitting across the table from you might have three bars, there's a good chance that your two bars are just as strong, if not stronger.

To more accurately gauge signal strength — say, for the optimal placement of a cell booster — the key is less acrobatics and instead, a better understanding of decibel-milliwatts (dBm). It's the most accurate and non-subjective signal strength measurement.

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What is dBm?

Decibel (dB) is a logarithmic unit used to represent the power and voltage strengths of electronic equipment. For example, signal boosters or the wires and cables that connect to radio and audio frequencies. In layman's terms, dB measures power intensity.

Because dB is logarithmic and therefore dimensionless, dBm is used as an absolute point of reference.

This means that power — in our case, signal strength — is measured with respect to one milliwatt. It can be calculated as ten times the log of the signal strength in milliwatts.

dB simply quantifies the ratio between two values, and those values are measured in dBm. So, once the dBm has been established, only then can you measure any change in dB.

Thanks to its ability to provide large and small values in short form, dBm is the measurement of choice for radio, microwaves, and fiber-optics networks. In the world of cellular boosters, dBm represents the strength of a signal at any given location.

What is a Good dBm Cell Signal?

Typically, a strong outside signal would clock in somewhere around -50 to -70 dBm. Anything below -100 dBm is considered weak. At -120 dBm, you'll experience extremely spotty signal (at best) or none at all.

The use of a signal booster could improve your outside dBm signal exponentially. For example, a home signal booster with up to +72 dB can take you from -116 dBm to -75 dBm. It's happened before. If you don't believe us, watch the video below. However, results will vary by situation.



According to the logarithm, signal strength doubles with every third decibel. So, something like -75 dBm is twice the power of -78 dBm. While the numbers don't reflect a significant change, the power actually increased exponentially. In our example, the signal became 26x more powerful with a signal booster.

How to Measure dBm on My Phone?

Signal strength apps are the easiest way to monitor and measure your dBm in real-time. An app we highly recommend is Network Cell Info Lite for Android devices. Unfortunately, there aren't any dBm measuring apps in the App Store. Sorry iPhone users.

The best way to measure cell phone signal strength on most iPhones is by accessing field test mode. For this to work, you must have a compatible carrier and chipset. Androids also have a field test mode function with decibel-reading capabilities.

Field Test Mode for iPhones:

For iOS 15:

  • Dial *3001#12345#*
  • Your dBm may be visible on the dashboard's RSRP section. If not…
  • Tap the Menu Tab on the top right corner.
  • Tap Cell Info.
  • Your dBm is read as rsrp.

For iOS 11, iOS 12, iOS 13, & iOS 14:

  • Dial *3001#12345#*
  • Tap LTE on iOS 11-13, or the Menu Tab on iOS 13-14
  • Tap Serving Cell Meas
  • Your dBm is read as rsrp0.

If you can't find your dBm reading, you most likely have an incompatible chipset. The following best method is performing speed tests inside and outside your home. This will help you determine where you receive the best signal. The App Store has many speed test apps. One of our favorites is OpenSignal.

Field Test Mode for Androids:

Field testing mode varies depending on the phone model and Android version. However, you will typically find it under Settings. Here's the typical sequence:

  • Tap Settings
  • Tap About Phone
  • Tap Status or Network
  • Tap SIM Status
  • Your dBm is under Signal strength

An accurate reading of your dBm isn't just good for optimizing the performance of cellular antennas and amplifiers. It will also make you sound like a true tech wizard when all your friends are flailing their phones around in search of those elusive bars.

What Can I Do If I Have Almost No dBm?

We highly recommend a cell phone signal booster. They are the most surefire way to combat bad signal. With the right cellular antennas, they can keep you connected in areas where it feels impossible.

Wilson Amplifiers is the leading provider of cellular enhancers for homes, offices, and vehicles. Our units are 5G ready and will enhance 4G and LTE signals for any phone with any carrier.

If you have any questions, whether it be about signal booster light patterns or something else, we're more than happy to help you end your signal issues. Email us today at [email protected] or call us at 1-800-373-2927.

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