Cell Signal Strength

Updated September 2019

What do the signal bars mean?

Signal bars are often not an accurate measurement of the strength of the signal your cell phone is receiving. While they do indicate the strength and quality of your reception, there’s no industry standard for this much signal equals this many bars—each cell phone manufacturer comes up with their own calculation. Because there are many different methods of computing bars, two different brands of phones on the same cellular network, placed next to each other, might display different numbers of bars.

Take a look at the notification bar at the top of this screen on a Samsung smartphone: The signal meter (circled in red) indicates 4 bars. Most people would say that’s very good signal. But is it?

Android smartphone screen with signal bars circled

How cell signal strength is actually measured

The signal your phone receives from a cell tower is measured in decibel-milliwatts (dBm), a unit of electrical power in milliwatts (mW) expressed on a decibel (dB) scale. There are the three things you need to know decibel-milliwatts:

  1. 1 milliwatt (1 mW) is equal to 0 decibel-milliwatts (0 dBm). Since cellular signal operates on much less power than 1 milliwatt (often as low as 0.00000000001 mW or less), signal strength is measured in negative dBm. The closer you get to 0 dBm, the stronger the signal; for example, −70 dBm is stronger than −90 dBm.
  2. The decibel-milliwatt scale is logarithmic, meaning that every change in 10 dBm is a tenfold change in mW (as shown in the table). So, −70 dBm is 10 times the signal strength of −80 dBm, 100 times that of −90 dBm, and 1,000 times that of −100 dBm.
  3. Any change in signal strength (gain or loss) is noted in decibels (dB). If your outside cell signal strength is −110 dBm, and you use a cell phone signal booster in your car that has 50 dB of gain, you’ll end up with −60 dBm of signal (−110 + 50 = −60, minus any signal loss from coax cables).
Power (dBm)
Power (mW)
−50 dBm
0.00001 mW
−60 dBm
0.000001 mW
−70 dBm
0.0000001 mW
−80 dBm
0.00000001 mW
−90 dBm
0.000000001 mW
−100 dBm
0.0000000001 mW
−110 dBm
0.00000000001 mW
−120 dBm
0.000000000001 mW

What’s considered “good” cell signal?

4G and 3G signal strength are measured differently:

  • 4G is measured using RSRP (Reference Signal Received Power).
  • 3G is measured using RSSI (Received Signal Strength Indicator).

In most instances, if you’re receiving less than −120 dBm RSRP or −100 dBm RSSI, you’ll be unable to make phone calls, send or receive text messages, or use Internet data.

How do I determine my cell signal strength?

Finding the signal strength received by your phone depends on the manufacturer, the phone model, and which cellular network you’re using.

Android instructions

If you have an Android smartphone, you can find your received signal strength in the phone’s settings under Signal Strength.

Exactly how to get this varies between phone models, but it’s usually somewhere in Settings > About Phone or Settings > System > About Phone. Some possible locations include:

  • Settings > About Phone > Status > Signal Strength
  • Settings > About Phone > Status > SIM Card Status > Signal Strength
  • Settings > System > About Phone > Status > SIM Status > Signal Strength

Here are some examples from Android phones in our office. (Notice that the RSRP readings in dBm are all nearly identical, but the number of bars varies.)

(click images to enlarge)

Signal strength reading on a Samsung Note 9 with Android 10 Signal strength reading on a Motorola Moto Z2 Play with Android 8 Signal strength reading on a Motorola Moto Z2 Play with Android 6

There are also many Android apps in the Google Play store that will display your phone’s signal strength. One that we recommend is Network Cell Info Lite, which shows your signal on its dashboard-like Guage screen:

Links to third-party software are provided “as is,” without warranty of any kind, either expressed or implied, and such software is to be used at your own risk. Powerful Signal will not be liable for any damages that you may suffer in connection with downloading, installing, or using such software.

iPhone instructions

Getting the cell signal strength reading on an iPhone may be possible, if your carrier and the chipset in your phone supports it.

Dial ✶3001#12345#✶ and press the Call button:

Dial *3001#12345#* to put an iPhone into Field Test Mode (iOS 11)

This will put your iPhone into Field Test Mode. You’ll see one of the three screens below:

If your Field Test Mode screen looks like this

Tap 1xEV-DO.

iPhone iOS 11 Field Test Mode screen for Qualcomm chips on Verizon or Sprint

On the next screen, look for the reading next to Rx AGC0.

iPhone iOS Field Test Mode 1xEV-DO screen for Qualcomm chips on Verizon or Sprint

To exit Field Test Mode, tap the left arrow icon in the top left-hand corner of your screen.

If your Field Test Mode screen looks like this

Tap LTE.

iPhone iOS 11 Field Test Mode screen for Intel chips on AT&T or T-Mobile

On the next screen, tap Serving Cell Meas.

iPhone iOS 11 Field Test Mode LTE screen for Intel chips on AT&T or T-Mobile

On the next screen, look for the reading next to rsrp0.

iPhone iOS Field Test Mode Serving Cell Meas screen for Intel chips on AT&T or T-Mobile

To exit Field Test Mode, tap the left arrow icon in the top left-hand corner of your screen.

If your Field Test Mode screen looks like this

Unfortunately this combination of chipset and carrier does not allow you to get a cell signal reading in dBm. You’ll have to take a signal reading with another iPhone, an Android phone, or a signal meter.

iPhone iOS 11 Field Test Mode screen for other chipsets and carriers

To exit Field Test Mode, tap the left arrow icon in the top left-hand corner of your screen.

Your cell signal will fluctuate

The signal strength you receive from the cell tower will constantly increase and decrease, even if you’re not moving. Standing still, you’ll commonly see fluctuations of ±5 dB. This is primarily due to two factors:

  1. The main cause is user load on the cell tower: The more people that are connected to one tower, the weaker the signal for all of them. Peak usage times (rush hour, lunch hour, etc.) will result in lower power for all users.
  2. Smartphones and other devices that use Internet data can also put considerable load on a tower.

Because of shifting usage loads, signal strength from a cell tower to your phone is constantly changing. If your cell signal is −110 dBm RSRP, you can probably make a call without any problems. If your −110 dBm signal falls to −120 dBm RSRP because of the load on the tower, you might drop a call but be able to redial and reconnect in a few seconds.

Physical barriers block cellular transmissions

It’s possible to be close to a cell tower but still have a weak cell signal. Many building materials—including concrete, metal, low-e glass, wood, and plaster—will reduce or block cellular frequencies from entering the building and reaching your phone. Stucco with wire mesh, metal roofs, large logs, and vapor barriers in attics also impede cell signals.

Even if you’re outdoors, dense forest, bluffs, and hills will reduce or block cell signals. Low areas around lakes, rivers, and gullies can have problems—there is signal, but it’s passing way over your head.

Dense urban areas with tall buildings have a different set of problems: Sometimes the top floors of buildings, 40 to 50 stories up, can’t get a good cell signal because towers are broadcasting at a lower elevation.

In all of these situations, a cell phone signal booster for home, office, or vehicle can solve your reception problems.

I can see the tower, but I have no signal

Sometimes you can see your carrier’s tower down the road or off in the distance, but you still have weak cell signal. Just because you can see the tower does not mean that the tower is broadcasting in your direction. This type of issue is more common along remote highways where cell signal is mostly directed toward the highway and little or none behind the tower.

Directional sector antennas used on cell towers broadcast signal only in certain directions. Just because you can see the tower does not mean that it sees you.

It’s also possible that the tower nearest you is operating for a different carrier than the one you’re using.

Frequency and technology limitations

Different cellular frequencies can travel different distances. Cellular transmissions in the 700 MHz (SMH) and 800 MHz frequency (CLR) ranges can travel more than twice the distance of transmissions at 1900 MHz (PCS) and 1700/2100 MHz (AWS).

700 and 800 MHz transmissions can also penetrate building materials better than 1900 and 1700/2100 MHz transmissions. You might be able to get 4G cellular service at 700 MHz inside a large, downtown building, but not get any PCS or AWS coverage (which have faster data speeds).

If you can find out which frequencies your carrier uses in your area, you might be able to discover the reason behind any reception issues you’re having.

Call Powerful Signal at 866‐912‐3444

…or contact us online. Our experts can help you determine why your cell phone signal may not be as strong as you need and help you find a solution to your problem.