It’s often useful to know how strong your iPhone’s cell signal is in certain areas. If you’re trying to make a call but it won’t go through or if you’re not getting the cell service you expect, then knowing your signal strength can help you determine why not.

Of course, virtually all phones have the “bars” graphic that displays on your home screen, so you know what your cell phone signal strength is. 

The problem with relying on those graphical representations for an indication of signal strength is that they are not backed by any standard. That means the accuracy of the dots or bars can vary widely.

Viewing your iPhone’s actual signal strength reading is always preferable to relying on how many bars are displayed on your iPhone. Signal strength is measured in dBm, or decibel milliwatts, a standard unit of measure, which is more accurate than bars.

By viewing the dBm reading on your iPhone you know with certainty how strong the signal is that you are receiving and whether the signal needs boosting. To see the dBm (signal strength) you must enter a sequence of commands to put your iPhone into ‘Field Test’ mode and display the reading.

How to Use iPhone Field Test Mode on iPhone X on iOS 12 or iOS 11

Follow the steps below to put your iPhone X into field test mode (These instructions should work for iOS 9 and up, but it may vary by carrier):

• Turn off your Wi-Fi before beginning
• Dial *3001#12345#*
• Press the call button
• Field test mode menu will show up

Now to find your iPhone X’s actual signal strength (dBm). There are two slight variations on how to access the dbm reading from here.

#1 If this screen below appears – Click on “Serving Cell Measurements”

#2 If this screen below appears – Tap on LTE then “Serving Cell Measurements”

#3 This step is the same now. Look for “rsrp0” – This number represents the dBm reading

The dBm number will range anywhere from -40 to -130, where -130 is the worst and -40 is the best signal strength.

So, the closer you are to -40 the better your cell signal will be. Now you finally have your accurate signal strength reading on your iPhone.

How to Use Field Test Mode on Older iOS Versions

If you have older iOS version then see below for field test mode instructions:

For Sprint or Verizon (or any iPhone with the Qualcomm chipset)

• For all models except iPhone X, first turn off LTE by going to Settings, then Cellular, then Cellular Data Options.
• Make sure Enable LTE status is Off. You can turn LTE on again after viewing the dBm reading.
• Tap on 1x EV-DO
• The dBm reading is the number identified as Rx AGCO
• You may have to restart your iPhone to get back into the menu.
• dBm is typically expressed as a negative number, -88 for example. The closer to zero the reading is, the stronger the cell signal. So a reading of -80 is stronger than -95.

For AT&T or T-Mobile (or any iPhone with the Intel chipset)

• Tap on LTE
• Tap 0n Serving Cell Measure
• The dBm reading is identified as rsrp0.

How to Disable Field Test Mode on iPhone

Now that you’ve figured out how to put your iPhone into field test mode, it’s very simple to disable it. First, go to everything you have open (by swiping up from the bottom of the screen and right) then swipe up (from bottom to top of the phone) with your finger to clear it.

Another option would be to just hit the back arrow once you’ve finished running the test.

iPhone Signal Strength Explained

The LTE signal strength your iPhone displays is not necessarily the same as the 3G or 1x signal strength since they’re on different frequencies. But the principle is the same – a dBm reading closer to zero represents a stronger signal.

A dBm reading of -50 is about the strongest signal you will see. When a signal is weaker than -100 dBm, that’s a pretty weak signal. If the signal gets much weaker than that, you likely won’t have service.

If you need to take dBm readings in several locations – to determine where the strongest cell signal is found, for example – you can put your iPhone into Airplane Mode for a few seconds after taking each reading. Doing this will reset your phone after each reading so the next dBm reading will be accurate.

To access Airplane Mode, swipe the screen from top to bottom. Then tap the airplane icon to turn on Airplane Mode. Wait 5-10 seconds, and then tap the icon again to turn it off.

How to Boost iPhone Signal

Once you’ve uncovered your actual signal strength using the instructions above, What can you do about poor cell signal?

One solution is to get an iPhone signal booster for your home or your vehicle, depending on where you are experiencing weak cell signal. An iPhone signal booster will take the weak cell signal from the outdoors and boost it into your home or vehicle. This will work for whichever cell carrier that you have and will give you instantly faster data and stronger signal strength. Say goodbye to annoying dropped calls and undelivered texts.