The display of Signal strength on iPhone is provided in the form of signal indicating bars; which can only be trusted to provide an approximate idea of cellular reception. Hence, if you are performing a diagnostic test or want to get an accurate representation of Signal strength, you need to access the “Field Test Mode” page or dashboard on iPhone; which displays the actual signal strength in Numbers (dBM) and provides other metrics related to the cellular data connection on your iPhone.
The Numbers indicate the Signal strength in decibels or decibel-milliwatts (dBm); which is the unit of measure for measuring Signal strength and this provides an accurate information about the actual signal strength on your device, compared to displaying signal strength in bars; which is known to vary between different models and carriers.
Related: How to Reduce Cellular Data Usage on iPhone.
Understanding Signal Strength Display in Numbers (dBm)
When you set iPhone to display signal strength in Numbers (dBm); you will see the signal strength appearing in the form of negative numbers (for example -88 dBM). Hence, closer the number to zero; the better the reception on your iPhone.
For example, when you move from an area of very bad signal strength to good signal strength, you are likely to see the signal strength numbers on your iPhone changing from -120 to -110, -100, -92, -75, -62 and so on.
When it comes to the actual signal strength on a mobile device, it is known to operate between -50 dBm to -120 dBm range and is considered as being excellent, good, weak or totally unusable; when it is between the following ranges.
- Excellent Signal: Between -50 to -79 dBm.
- Good to Fair Signal: Between -80 to -99 dBm.
- Weak Signal: Between -100 dBm or lower.
- No Service: -120 dBm.
Note: If you are interested in this subject, you can refer to this link on Wikipedia for more information.
1. Display Signal Strength in Numbers on iPhone
The first step that is required to display the signal strength in numbers (dBm) for diagnostic testing is to disable the Wi-Fi network on iPhone. While this is not a technical requirement, disabling Wi-Fi is necessary to get an accurate reading and prevent the possibility of the status bar display being impacted by a strong Wi-Fi network.
After disabling Wi-Fi, you can make iPhone to display its mobile or cellular signal strength in Numbers by dialing *3001#12345#*, which takes you to the “Field Test Mode” page; displaying the actual signal strength on your device in decibel-milliwatts (dBm) for 5G, LTE and other available bands.
1. Go to Settings > Wi-Fi > Move the Wi-Fi Slider to OFF position.
2. After disabling Wi-Fi, open the Phone App on your iPhone.
3. Use the Keypad to type *3001#12345#* and press the Call button.
4. This will take you to iPhone’s FTM (Field Test Mode) Dashboard, where you will be able to see the signal strength of both 4G & 5G network on your iPhone being displayed in the RSRP Tab.
As you can see in above image, the iPhone signal strength is -88 dBm, which can be considered as being an acceptable or Fair Signal strength.
2. Change Signal Strength Display from Bars to Numbers (dBm)
While it is not possible to actually change the Signal strength display from Bars to Numbers (dBm) in the current version of iOS; this feature was available in the older versions of iOS.
If you have an older device (iOS 10 and below), you should still be able to change the display of Signal strength from bars to Numbers (dBm) by using the following steps.
1. Go to Settings > Wi-Fi > Disable Wi-Fi by moving the slider to OFF position.
2. Open Phone App > Dial 3001#12345#* and press the Call button.
3. Hold down the Power button, until you see “Slide to Power OFF” screen.
4. Press and Hold-down the Home button, until you see the screen going blank.
After few seconds; you should see your device returning back to Home screen, displaying the Signal strength in numbers (dBm).