How to see your true cellular signal strength with the iPhone Field Test app

Signal bars don’t tell you as much as you think. If you really want to know the strength of your cell signal, use this hidden app.

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Sometimes you have two bars but can’t load any webpages. Sometimes you have four bars, but your friend with a different phone on the same network has only two. We’ve become reliant on signal bars to tell us how strong our cellular connection is, but in truth, the bars are bullshit.

Those signal bars are almost completely arbitrary. Yes, more bars should mean a stronger signal, but there is no standard scale. Every phone manufacturer gets to decide how much signal strength equals how many bars, and it often varies widely from model to model.

If you really want to know how strong your cell signal is, you need to look at a direct measurement of the signal strength, as measured in decibels (dB). Fortunately, there’s a hidden “Field Test” menu on your iPhone to do just that. It’s not particularly convenient, but it is interesting.

How to access the Field Test menu

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Turn off your Wi-Fi before accessing the Field Test application.

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The Field Test menu has changed along with iOS over the years, but this guide should work for anyone on iOS 11 or iOS 12.

First, open the Control Center (or head over to the Settings app) and turn off Wi-Fi. 

Then, open the Phone app and enter in the following numbers and symbols, exactly as written (including the stars and pound signs):

*3001#12345#*

Press the call button, and the Field Test menu will pop up on screen.

Using Field Test to see your cell signal strength

Now that you’re in this weird Field Test menu, how do you check your cellular signal strength?

There’s a lot of stuff in here, and it’s not very well labeled. After all, this is not a menu for regular users, but for service technicians.

Start by choosing “LTE” from the first menu.

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Choose LTE first.

Then look for menu labeled “Serving Cell Meas.” This will contain measurements taken from the “serving” cell—the one you’re currently connected to.

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Next, select Serving Cell Meas

Selecting Serving Cell Meas will take you to a page of data. You’ll notice the order of the listing here changes every few seconds, as the measurements continually update.

You’re looking for “rsrp0,” which is the Reference Signal Received Power for the tower closest to you (although you may be connected to a secondary, further tower, whose power is listed under “rsrp1”).

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The figure you should be most concerned with is rsrp0.

This should be a negative number, in a range from around -40 to -140. A number closer to -40 is a really strong signal, while a number closer to -140 is a really poor signal. Anything between -40 and -80 is very good and you shouldn’t have any signal problems. Anything below -120 is very poor, and you might suffer interruptions in your connection and very poor data speeds.

There’s another useful data point on this page, labeled RSRQ0 (Reference Signal Received Quality). This is a value derived from both the signal strength and interference. This usually ranges between -3 (good) and -19.5 (bad). It’s possible to have a lower number, but to do so you have to have a really noisy, low-power signal. 

This story, "How to see your true cellular signal strength with the iPhone Field Test app" was originally published by Macworld.

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