How to Check Coverage Before You Switch (Without Trusting the Map)

Every coverage complaint I have ever handled traced back to the same mistake: someone looked at a colorful map, saw their town shaded in, and assumed they were covered. Coverage maps are modeled predictions, not measurements. They do not know about the hill behind your house, the metal roof on your office, or the fact that the nearest tower is congested every weekday at 5 p.m. This guide is the process I use to check coverage properly, and it costs nothing.

Understand what a coverage map is telling you

A carrier map is generated from tower locations, transmit power, terrain data, and propagation modeling. It answers 'should a signal theoretically reach here', not 'will your phone work indoors on a Tuesday'. Two things the map almost never reflects: building materials and network congestion. Low-E windows, stucco with wire mesh, concrete, and metal roofing all attenuate signal dramatically. Congestion is invisible on any map — a tower can show full bars and still crawl at peak hours.

• Full bars measure signal strength, not speed or capacity
• Indoor performance can be 10–30 dB worse than outdoor at the same address
• Roaming coverage may appear on a map but come with data restrictions
• Maps update slowly and rarely reflect recent congestion or tower changes

Step 1: Read your current phone's actual signal number

Bars are a marketing abstraction; the real number is RSRP, measured in dBm, and your phone already knows it. On an iPhone, field test access varies by iOS version, but on most Android phones you can find it in Settings, then About phone, then SIM status or Network. Look for 'Signal strength' in dBm. A value around -85 dBm is strong, -100 dBm is workable, -110 dBm is marginal, and anything past -115 dBm will drop calls. Write down the number in the three rooms where you actually use your phone.

Step 2: Check the independent data, not just the carrier

Use the FCC's National Broadband Map, which collects carrier-reported mobile coverage and lets you view it by address, and cross-reference with crowdsourced measurement sites that plot real user speed tests. Crowdsourced data has its own biases — it over-represents places people run speed tests — but two independent sources disagreeing with a carrier's own map is a meaningful signal. Ask neighbors and coworkers on the carrier you are considering what their experience is at that exact address.

• FCC National Broadband Map — address-level, carrier-reported, free
• Crowdsourced speed-test coverage layers — real measurements, uneven density
• Local community groups — the fastest way to learn a neighborhood dead zone
• The carrier's own map — useful as a fourth opinion, not a first

Step 3: Test before you port, not after

This is the part almost nobody does, and it is the part that makes the whole thing safe. If your phone supports eSIM, you can add a second line on the carrier you are considering while your existing number keeps working normally. Run it for a week as a test line. Carry it through your real life: your house, your bedroom, your basement, the office, the grocery store, the commute. Only after it passes do you move your primary number.

• Add the prospective carrier as an eSIM second line
• Set the test line as your data line for a few days and watch how it behaves
• Place several voice calls, ideally indoors and in the car
• Run speed tests at your peak-usage hour, not at 6 a.m.
• Test the specific rooms where you actually take calls
• Only port your main number once the test line has earned it

Step 4: Know your fixes if coverage is only weak indoors

Weak indoor coverage on an otherwise good network is a solvable problem. Wi-Fi calling routes voice over your home internet and is free on essentially every modern carrier and phone — turn it on before you conclude a carrier is bad. Beyond that, a signal booster amplifies an existing outdoor signal indoors, but it needs something to amplify; if you have nothing outside, a booster will not invent it. Some carriers also offer femtocell-style devices that create coverage from your broadband connection.

Step 5: Keep an exit route

Before you port, note your account number and transfer PIN from your current carrier, and understand that a completed port automatically closes the old line. If coverage turns out badly after the fact, you can port back, but it is a hassle — which is exactly why the eSIM test week in step three is worth the small effort. Prepaid plans make this easier than postpaid, because there is no contract holding you in place and no device balance to unwind.

Coverage is hyper-local. The only map that matters is the one you draw yourself, walking through your own house with a real line active.