1. Mobile data call quality
The test above runs the same latency, jitter, loss and speed checks as the main VoIP test, tuned for a phone. Turn Wi-Fi off first so you test the carrier's network. Wi-Fi calling, softphone apps, Teams and Zoom all ride on this data connection.
2. Grade your signal
Open your phone's field test screen
| Phone | How | What to look for |
|---|---|---|
| iPhone | Open the Phone app, dial *3001#12345#*, press Call | RSRP, RSRQ and SINR under the serving cell (layout changes between iOS versions) |
| Android (most) | Settings → About phone → SIM status (or Status) → Signal strength; or dial *#*#4636#*#* on many models | Signal strength in dBm; the testing menu on many models shows RSRP/RSRQ/SINR |
| Any phone | Dial *#06# | IMEI — needed when a carrier or tech troubleshoots the handset |
Codes and menu paths vary by manufacturer, carrier and software version. If a code doesn't work on your model, there's no harm — it simply won't open.
Signal reference (LTE / 5G NR)
| Excellent | Good | Fair | Poor | |
|---|---|---|---|---|
| RSRP (strength) | ≥ −80 dBm | −80 to −90 | −90 to −100 | ≤ −100 |
| RSRQ (quality) | ≥ −10 dB | −10 to −15 | −15 to −20 | ≤ −20 |
| SINR (signal vs. noise) | ≥ 20 dB | 13 to 20 | 0 to 13 | ≤ 0 |
These are common field-engineering rules of thumb. There is no single official scale; carriers and equipment vendors use slightly different cutoffs.
3. A simple dropped-call test
- Note your RSRP and SINR at your desk.
- Call a landline or another cell phone and keep talking while you walk your normal routes: desk, conference room, break room, warehouse, parking lot.
- Note where audio breaks up or the call drops, and the signal readings at that spot.
- Repeat on Wi-Fi calling. If Wi-Fi calling fixes it, the building is blocking the carrier; if not, check the Wi-Fi network with the VoIP test.
Fixes for poor cell coverage at work
- Wi-Fi calling — free, built into most phones; quality depends on your Wi-Fi and internet.
- A business softphone app — runs your office extension on the phone over data or Wi-Fi.
- A cellular signal booster — an outside antenna, amplifier and inside antennas. Consumer boosters must be FCC-certified and registered with your carrier; installation and antenna placement decide whether they work.
- Check the carrier maps — the FCC National Broadband Map shows reported mobile coverage by provider.
Frequently asked questions
How do I test my cell phone call quality?
Turn Wi-Fi off and run the cellular data test on this page to measure latency, jitter, loss and speed on the carrier's network. Then open your phone's field test screen to read RSRP, RSRQ and SINR, and enter them in the signal grader. Finally, make a test call while walking the building to find dead spots.
What is a good cell signal strength in dBm?
On LTE and 5G, RSRP of −80 dBm or higher is excellent, −80 to −90 dBm is good, −90 to −100 dBm is fair, and −100 dBm or below is poor. Numbers closer to zero are stronger. Signal quality (RSRQ and SINR) matters too — a strong but noisy signal still drops calls.
How do I see my real signal strength on iPhone?
Open the Phone app, dial *3001#12345#* and press Call to open Field Test Mode. Look for RSRP, RSRQ and SINR for the serving cell. The layout differs between iOS versions.
How do I check signal strength on Android?
On most Android phones go to Settings, About phone, then SIM status or Status, and look at Signal strength in dBm. On many models, dialing *#*#4636#*#* opens a testing menu with more detail. Menu names vary by manufacturer.
Why do my cell phone calls drop inside my building?
Building materials block cellular signals — metal roofs and siding, concrete, brick, and energy-efficient low-E glass are the usual culprits. The phone may also be far from the tower or on a crowded cell. Wi-Fi calling, a softphone app, or a properly installed signal booster are the standard fixes.
Do signal bars mean anything?
Only roughly. There is no industry standard for how many bars equal what signal level, and each manufacturer and carrier maps them differently. The dBm readings in field test mode are the reliable measurement.
Is Wi-Fi calling better than cellular?
Inside a building with weak cell signal, Wi-Fi calling is usually better, as long as the Wi-Fi and internet connection are good. Outside or on the move, cellular (VoLTE) is usually more reliable. Phones can hand calls between the two, but handoff isn't perfect on every phone and carrier.
Are cell phone signal boosters legal?
Yes, if the booster is FCC-certified and you register it with your wireless carrier, as FCC rules require for consumer boosters. Improperly installed or uncertified boosters can interfere with the carrier's network.
Sources & references
- FCC National Broadband Map (fixed and mobile coverage)
- FCC — Signal boosters consumer guide
- MDN — Network Information API
Written by Eric · Reviewed November 2026