Signal strength is the power of the radio signal received by a phone, modem or other device from a base station, usually expressed in decibel-milliwatts (dBm). In network performance and telecommunications, it describes how much useful energy from the serving cell actually reaches the antenna, and it is the first value engineers check when a connection is slow, unstable or drops entirely.
Signal strength is necessary but not sufficient for good service. A device can show strong reception and still deliver poor throughput when interference, noise or congestion degrade the link, which is why modern networks report several related metrics alongside raw power.
How signal strength is measured
Signal strength is measured as received power on a logarithmic scale, because radio power falls by many orders of magnitude between the transmitter and the receiver. The unit dBm expresses power relative to one milliwatt: 0 dBm is 1 mW, -30 dBm is one microwatt, and a typical phone receives a cellular signal somewhere between -50 dBm and -120 dBm. Because the scale is logarithmic, a change of 3 dB doubles or halves the power, and a change of 10 dB means a factor of ten.
Each radio generation defines its own measurement. In 2G networks the device reports RxLev, in 3G it reports RSCP for the pilot channel, and in 4G LTE and 5G NR it reports RSRP, the average power of the reference signals within a single resource element. Wi-Fi devices report RSSI, which is total received power across the channel and therefore includes noise and interference.
The following table summarizes the main signal strength metrics and the technologies that use them.
| Metric | Technology | What it measures | Typical range |
|---|---|---|---|
| RxLev | GSM (2G) | Received power on the broadcast carrier | -110 to -48 dBm |
| RSCP | UMTS (3G) | Power of the common pilot channel | -120 to -25 dBm |
| RSRP | LTE (4G) | Average power per reference signal element | -140 to -44 dBm |
| SS-RSRP | NR (5G) | Power of synchronization signal block elements | -156 to -31 dBm |
| RSSI | LTE, Wi-Fi | Total power in the channel, including noise | -100 to -20 dBm |
What determines the received power
Received signal strength is the transmit power minus all losses along the path, plus antenna gains at both ends. Engineers capture this in a link budget, which adds the base station output, antenna gain and receiver gain, then subtracts path loss, penetration loss and cable or body losses to predict the level a device will see.
Free-space path loss grows with the square of distance and with frequency, so higher frequency bands lose more power over the same distance. A 700 MHz signal travels farther and penetrates buildings better than a 3.5 GHz signal, and millimeter-wave bands around 26 to 28 GHz cover only short distances with clear line of sight. Real environments add shadowing from terrain and buildings and multipath fading, where reflected copies of the signal combine and cancel over distances as small as half a wavelength.
The table below lists the main factors that reduce received power and their typical magnitude.
| Factor | Typical loss | Notes |
|---|---|---|
| Distance from the cell | Tens of dB per few kilometers | Increases with frequency |
| Exterior wall | 5 to 20 dB | Concrete and brick are worst |
| Low-emissivity glass | 20 to 40 dB | Metallic coatings block radio waves |
| Vehicle body | 5 to 15 dB | Depends on windows and coatings |
| Hand and head of the user | 3 to 10 dB | Depends on grip and antenna position |
| Basement or elevator | 20 dB or more | Often creates a dead zone |
Interpreting signal strength values
Signal strength values are interpreted against practical thresholds rather than a fixed pass or fail line. For LTE and 5G, an RSRP above -80 dBm is excellent, values between -80 and -100 dBm usually support good service, and readings below -110 dBm indicate the cell edge, where throughput falls and calls may drop. The exact limits depend on the band, the receiver sensitivity and the amount of interference.
| RSRP range | Rating | Typical user experience |
|---|---|---|
| Above -80 dBm | Excellent | Full speed, stable video calls |
| -80 to -90 dBm | Good | Reliable data and voice |
| -90 to -100 dBm | Fair | Usable, speeds vary with load |
| -100 to -110 dBm | Poor | Slow data, occasional failures |
| Below -110 dBm | Very poor | Frequent drops, near no service |
The signal bars on a phone are a rough visual summary of these values. Manufacturers and operating systems map dBm to bars differently, so two phones showing the same bars can be receiving quite different power. For any serious diagnosis, the numeric value from a field test mode or diagnostic app is the reliable reference.
Signal strength compared with signal quality
Signal strength measures how much power arrives, while signal quality measures how clean that power is. The neighboring metrics RSRQ and SINR describe quality: RSRQ relates reference signal power to total received power, and SINR compares the wanted signal with interference plus noise. A device near several overlapping cells can have strong RSRP but low SINR, because neighbors on the same frequency add interference.
| Metric | Question it answers | Good value | Main limitation |
|---|---|---|---|
| RSRP | How strong is the serving cell | Above -90 dBm | Ignores interference |
| RSRQ | How loaded and clean is the channel | Above -10 dB | Changes with cell load |
| SINR | How much stronger is the signal than interference | Above 13 dB | Varies quickly with movement |
| RSSI | How much total energy is present | Context dependent | Mixes signal and noise |
Throughput depends mainly on SINR, because the radio chooses its modulation and coding scheme from the measured channel quality. High SINR allows dense modulation such as 256-QAM, while low SINR forces robust but slow schemes. Strength still matters, since SINR cannot exceed what the noise floor permits at a given power level.
Improving weak signal strength
Weak signal strength is improved either by reducing losses or by bringing the transmitter closer. Simple measures include moving toward a window, using a higher floor, or placing a fixed wireless router where measurements are best. Operators add sites, lower bands or small cells; building owners can install distributed antenna systems or operator-approved repeaters.
- Wi-Fi calling routes voice over a home broadband link when indoor cellular coverage is weak.
- External directional antennas on fixed wireless routers can add 6 to 15 dB of gain toward the cell.
- Femtocells and small cells create local coverage connected through a wired backhaul.
- Unapproved boosters can amplify noise and interfere with the network, and are illegal in many countries.
Common mistakes in reading signal strength
The most common mistake is treating bars as a speed indicator. Full bars on a congested cell can deliver lower throughput than two bars on an idle one, and a speed test reflects backhaul and server performance as well as radio conditions. Another frequent error is comparing RSSI with RSRP directly; RSSI is always higher because it sums power over the whole channel bandwidth.
Single readings also mislead, because fading causes fluctuations of 10 dB or more within seconds. Reliable assessment uses averages over time and location, records the band and cell identity, and pairs strength with RSRQ or SINR before drawing conclusions about network capacity or coverage.
The idea in brief
Signal strength tells you how loud the network sounds to your phone. The tower sends out radio waves, and by the time they reach you, most of their energy has faded because of distance, walls and obstacles. The phone measures what is left, and that number is the signal strength.
A loud signal is helpful, but it is not everything. Think of talking to a friend in a crowded restaurant: you may hear their voice clearly, yet the noise around you still makes the conversation hard. Strength and clarity together decide how well your connection works.
A practical scenario
A small accounting office on the ground floor of a concrete building complains that mobile calls drop and data is slow. A technician opens a diagnostic app and records an RSRP of -112 dBm on the 1800 MHz band indoors, compared with -85 dBm on the sidewalk outside. The difference of about 27 dB points to heavy building penetration loss, partly caused by coated windows.
The office installs a fixed wireless router with an external antenna on the roof, which receives around -78 dBm, and enables Wi-Fi calling on staff phones. Call drops stop and data speeds become consistent, without any change to the operator network.