A percentage is an estimate, not a radio unit
dBm is a logarithmic power measurement. Phones and carriers use their own thresholds, smoothing and quality inputs for bars, so no universal formula converts dBm into an official percentage.
This calculator uses transparent reference ranges
RSRP is mapped from -120 dBm at 0% to -80 dBm at 100%. RSSI is mapped from -110 dBm to -60 dBm. Values outside the range are clamped rather than presented as impossible percentages.
Power does not equal speed
Interference, RSRQ, SINR, network load, spectrum and backhaul can make a strong power reading perform poorly. Use the percentage only as a quick comparison between controlled measurements.
Frequently asked questions
What percentage is -100 dBm RSRP?
With this practical -120 to -80 dBm scale, -100 dBm is about 50%. The iPhone signal bars may use different thresholds.
Is 100% signal always fast?
No. It represents strong received power on the selected scale, not available network capacity or low interference.
Should I use RSRP or RSSI for LTE and 5G?
RSRP is usually more useful for LTE and 5G reference-signal power. Use RSSI only when that is the measurement you actually have.