[willidiots]

To TFA's point - "Bars" are relative and relatively meaningless - [SS]RSRP, RSRQ and SINR are your real numeric signal strength / quality measurements.

Not sure about Apple, but on Android, individual carriers can set the number-to-bars thresholds. Two otherwise-identical signals could be represented as a different number of bars depending on your particular carrier: https://source.android.com/docs/core/connect/signal-strength