Signal strength at a glance (4G RSRP)
- −80 dBm or better: excellent — full bars, clear HD calls.
- −80 to −90 dBm: good — reliable calls and data.
- −90 to −100 dBm: fair — calls work, data slows.
- −100 to −110 dBm: poor — drops and crackling.
- Below −110 dBm: very poor / dead zone — calls fail.
- Closer to zero is stronger: −75 dBm is much better than −105 dBm. Every 10 dB is ten times the power.
What is dBm and why is it negative?
dBm measures received radio power relative to one milliwatt. Mobile signals are tiny fractions of a milliwatt, so the numbers are negative — and the closer to zero, the stronger the signal. The scale is logarithmic: a reading 10 dB higher means ten times more power, and 3 dB means twice as much. That is why moving from −110 dBm to −90 dBm feels like night and day.
Bars are only a rough summary, and each phone brand maps bars differently. Two phones on the same network in the same room can show different bars but nearly the same dBm. For decisions — like whether to buy a booster — dBm is far more reliable.
How to check signal strength in dBm on your phone
On Android
- Open Settings → About phone → SIM status (on some phones: Status information → SIM status). “Signal strength” shows dBm and asu.
- Alternatively dial
*#*#4636#*#*and open Phone information. Many phones show signal strength or RSRP here; some brands disable this menu. - A free cell-info app can also show RSRP, RSRQ, SINR and the band number.
On iPhone
- Dial
*3001#12345#and press call to open Field Test mode. - Open the LTE section, then Serving Cell Meas, and read rsrp. Menu names vary between iOS versions.
Where to measure
Take one reading where the signal is worst indoors, and one outside — on the roof, terrace, balcony or at an open window. Stand still for 10–15 seconds at each spot; readings bounce around. The outdoor reading tells you whether a booster has anything to work with; the difference between outdoor and indoor tells you how much your building is blocking.
Mobile signal strength chart (4G / LTE)
| RSRP | Rating | What you’ll notice |
|---|---|---|
| −80 dBm or higher | Excellent | Full bars, HD voice, fastest 4G |
| −80 to −90 dBm | Good | Reliable calls and data |
| −90 to −100 dBm | Fair | Calls OK, data noticeably slower, occasional drops |
| −100 to −110 dBm | Poor | Call drops, “call cracking”, slow or stalled data |
| Below −110 dBm | Very poor / dead zone | Calls fail to connect, frequent “No service” |
These bands are widely used rules of thumb for LTE. 2G and 3G readings (RSSI or RSCP) use a different scale, so a 3G reading of −85 dBm isn’t directly comparable with 4G RSRP.
RSRQ and SINR: signal quality, not just strength
| Measure | Good | Fair | Poor | What it means |
|---|---|---|---|---|
| RSRP (dBm) | −90 or higher | −90 to −105 | below −105 | How strong the tower’s signal is |
| RSRQ (dB) | −10 or higher | −10 to −15 | below −15 | Signal quality, affected by load and interference |
| SINR (dB) | 13 or higher | 0 to 13 | below 0 | How clean the signal is compared with noise |
Full bars but calls still crackle? That’s usually poor SINR/RSRQ — common on upper floors of high-rises where the phone hears many towers at once. A booster with a directional outdoor antenna aimed at one tower can help there too.
Will a signal booster help my reading?
A booster amplifies the signal available outside and rebroadcasts it indoors, so the outdoor reading decides:
- Outdoor −100 dBm or better: a good candidate. A correctly matched booster can usually bring that signal into the rooms where it’s weak.
- Outdoor −100 to −110 dBm: workable with a directional LPDA antenna and a higher-gain model.
- Outdoor −110 to −115 dBm: borderline. Height and antenna direction make the difference — share your readings with us before buying.
- Outdoor below −115 dBm or no signal: a booster is unlikely to help. Consider Wi-Fi calling — see signal booster vs Wi-Fi calling.
- Indoor already better than −90 dBm but problems persist: the cause is more likely congestion or a phone setting (VoLTE off, old SIM) than weak signal.
Once you know a booster will help, the signal booster finder recommends the right SIGLIFT model for your operator and area. For villages and distant towers, read network booster for village; for below-ground dead zones, see basement signal booster.
Why is my indoor signal so much worse than outside?
Buildings absorb signal. A brick or RCC wall can cost 10–20 dB, energy-saving glass a similar amount, and a basement 20–40 dB. If your outdoor reading is −90 dBm and your bedroom shows −115 dBm, the building is taking 25 dB — over 99% of the signal. That gap is exactly what a booster makes up.
