Here you go. All Apple devices have a field test mode...
For iPhone with Intel Chipset (
iOS 11, iOS 12, iOS 13, and 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.
dBm is what you're looking for:
Cell signal strength ranges from -50 dBm to -120 dBm for all cellular devices. Typically:
-50 to -79 dBm = great signal (4 to 5 bars).
-80 to -89 dBm = good signal (3 to 4 bars).
-90 to -99 dBm = average signal (2 to 3 bars).
-100 to -109 dBm = poor signal (1 to 2 bars).
-110 to -120 dBm = very poor signal or a dead zone (0 to 1 bar).
dBm readings are not subjective. They don’t fluctuate based on carriers or manufacturers. The closer you are to -50 dBm, the better your signal. For those closer to -120 dBm, a signal booster or repeater will help improve your service.