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Field Test Mode on iPhone allows users to get detailed information on their cellular signal and cellular connection, and has long been a popular alternate method of displaying the cell signal on iPhones as a number instead of the signal bars or dots. Field Test Mode is undeniably for more advanced purposes, but some casual iPhone users found value in it as well in order to find a consistently reliable cellular signal.
But ever since iOS 11 and new iPhone models, Field Test Mode is different from how it used to be, and if you enter Field Test Mode in iOS 11 you will not immediately see the numerical dBm cell signal indicator replacing the bars.
Not to worry, you can continue to see the cellular signal as numbers on iPhone with Field Test Mode in iOS 11, it just works a bit differently than it did before in prior versions of system software.
How to Use Field Test Mode in iOS 11 to See Number Cell Signal Strength on iPhone
The iPhone must have an active cellular connection to be able to access and use Field Test Mode to measure the signal strength, the rest is easy:
- Open the “Phone” app on your iPhone and enter the following number exactly:
- Press the Call button to dial the number, this will immediately launch the hidden “Field Test Mode” app on the iPhone
- Tap on “LTE”
- Tap on “Serving Cell Meas”
- Look for “rsrp0” and the number corresponding will be the numerical measurement of the iPhone cellular signal strength in dBm
RSRP stands for Reference Signal Received Power and is a variation of RSSI measurement.
RSRQ stands for Reference Signal Received Quality.
Supposedly rsrp0 is the primary cell tower connected to, and rsrp1 is the next closest cell tower (or one with the strongest connection anyway), each obviously has their own cellular signal strength depending on power, connection, distance, interference, and other measures.
As for the numbers, which are measured in dBm, they will range from -40 to -130, with -40 being the best possible signal and -130 being the worst. Generally speaking, once you start approaching -110 or lower you will find the cell service is spottier and voice conversations may sound garbled or have aspects cutting out, whereas if you’re at -80 or so your signal should be pretty good and not have any issues.
Field Test Mode has a lot of data available, much of which is going to be completely useless or befuddling to the average iPhone user, much less anyone who is not a field test engineer or operator (and I am neither). For the geekier folks who are interested in numerical measurements of their cellular signal, “Serving Cell Meas” and “LTE Neighbor Cell Meas” are likely the two most pertinent sources of information, since both of those will reveal numerical cellular signals akin to what used to be displayed by default in Field Test Mode before iOS 11.
Note that accessing the dBm numerical cellular signal details may vary per iPhone model and cellular carrier, with some cellular providers not easily sharing this information through Field Test Mode. The approach above was walked through on an iPhone X with the latest iOS 11.x release on AT&T with an LTE signal, but if you want to view other GSM or UMTS signals then you’d look for the appropriate selection within the Field Test Mode app on iPhone.
And yes, at least at the consumer level, this is the only way to access Field Test Mode on the iPhone, and it has been that way for quite some time.
How do I get the signal numbers to replace the bars on iPhone X, or iOS 11?
Many users want to replace the bar signal indicator with the signal numbers instead, since the numerical reception indicator is more accurate. Unfortunately this is not possible in current versions of iOS or on the newest iPhone models with late iOS software. As of now, only iOS version before iOS 11 can use the numerical reception indicator as a replacement for the cell signal reception bars. If you want to learn how to do that on an earlier device with an older iOS release, go here to do so.