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How cell signal strength is actually measured
The signal your phone receives from a cell tower is measured in decibel-milliwatts (dBm), a unit of electrical power in milliwatts (mW) expressed on a decibel (dB) scale. 1 mW is equal to 1⁄1000th of a watt (W).
There are the three things you need to know about decibel-milliwatts:
- 1 milliwatt (1 mW) is equal to 0 decibel-milliwatts (0 dBm). Since cell phones often receive less than 1 milliwatt of signal strength from a cell tower—sometimes as low as 0.00000000001 mW or less—cell signal strength is less than 0 dBm and therefore measured in negative numbers.
The closer you get to 0 dBm, the stronger the signal; for example, −70 dBm is stronger than −90 dBm, −95 dBm is stronger than −105 dBm, and so forth. - The decibel-milliwatt scale is logarithmic, meaning that every 10 dBm is a tenfold change in milliwatts:
−120 dBm
0.000000000001 mW
- Any change in signal strength—gain or loss—is indicated in decibels (dB). If your outside cell signal strength is −110 dBm, and you use a cell phone signal booster in your car that provides 50 dB of gain, you’ll receive −60 dBm of signal* (−110 dBm + 50 dB = −60 dBm).
What’s considered “good” cell signal?
4G and 5G cellular signal strength are measured using RSRP (Reference Signal Received Power). Excellent signal strength on the RSRP scale is anything stronger than about −85 dBm; poor signal strength is anything less than about −115 dBm:
If you’re receiving less than −120 dBm RSRP, you’ll probably have difficulty making phone calls, sending or receiving text messages, or using internet data.
Another factor to keep in mind is the quality of your cellular connection—how much usable signal you are receiving vs. the amount of interference or noise (unwanted disturbances of the signal). There are ways to measure cellular signal quality—see our Knowledge Base article for more about that—but the important thing to know is that you can have strong cellular signal and still have slow data and dropped calls because your signal quality is poor.
How do I measure my cell phone signal strength?
Finding the signal strength received by your phone depends on the manufacturer, the phone model, and which cellular network you’re using.
Android instructions
If you have an Android smartphone, look in the phone’s settings under Signal Strength.
Exactly where this is found varies between phone models, but it’s usually somewhere in the phone’s settings; possible locations include:
- Settings > About Phone > SIM Status > Signal Strength
- Settings > About Phone > Status > Signal Strength
- Settings > About Phone > Status > Sim Card Status > Signal Strength
- Settings > System > About Phone > Status > Sim Status > Signal Strength
Here are some examples from Android phones in our office. (Notice that the RSRP readings in dBm are all nearly identical, but the number of bars varies.)
