Field test mode is a wonderful and hidden feature on iPhones that lets you convert those somewhat inaccurate signal bars (or dots) into a much more precise number.
The following video from Tech Insider does a great job of walking you through how to turn on Field Test Mode on your iPhone. We've also outlined the necessary steps as well.
- Dial: *3001#12345#* and then press the call button.
- Your phone will now show a number instead of the bars/dots in the top left corner.
- Hold down the power button on the phone until the "power off" screen shows.
- Press and hold down the round select button on your phone for 6 seconds.
- Your phone will go back to the home screen and now you will continue to see the numbers for your signal strength.
You can tap on the numbers to have it show the bars instead, so you can now easily see your true signal and compare that to how many bars you are seeing.