How to Test Cell Signal Strength on iPhone or Android

This guide shows you how to check the actual cellular signal strength on your iPhone or Android phone, going beyond the bars to see the precise dBm and ASU values. You’ll learn the built-in field test modes, how to read the numbers, and what to do if your signal is weak. No extra apps or tools are required—just your phone.

What You’ll Need

• An iPhone (any model with iOS 11 or later) or an Android phone (any recent version).
• A SIM card inserted and an active cellular plan (Wi-Fi calling can be enabled, but the test measures cellular only).
• About two minutes of time—the field test mode is hidden but quick to access.

Step-by-Step

On an iPhone

1. Open the Phone app. Tap the keypad tab at the bottom.
2. Dial the field test code. Type *3001#12345#* and press the green call button. The screen will switch to the Field Test app automatically.
3. Check the signal reading. Look at the top-left corner of the screen—you’ll see a negative number like -85 or -110. That’s your signal strength in dBm (decibel-milliwatts). If you only see bars, tap the signal indicator to switch it to the numeric display.
4. Exit the field test. Press the Home button or swipe up from the bottom to leave the app. The numeric readout may persist in the status bar; to revert to bars, tap the number again or restart your iPhone.

On an Android Phone

1. Open the Settings app. Scroll down and tap About phone (or About device on some models).
2. Find the status information. Tap Status or Status information, then look for SIM card status or Network. The exact menu names vary by manufacturer and Android version.
3. Read the signal strength. You’ll see two numbers: Signal strength (in dBm, e.g., -87) and Signal strength (ASU) (a number like 12). The dBm value is what you want—the closer to 0, the better.
4. Use the dialer method (alternative). On many Android phones, you can open the Phone app and dial *#*#4636#*#* to open a testing menu. Tap Phone information and look for the signal strength there. This doesn’t work on all models, so if nothing happens, stick with Settings.

Common Mistakes

• Confusing dBm with ASU. dBm is the actual signal power (a negative number). ASU is a scaled index (0–31 for LTE). Don’t compare ASU values across different network types—always use dBm.
• Testing with Wi-Fi on. If you’re connected to Wi-Fi, the phone may route data through Wi-Fi and the cellular radio can go idle, giving a misleading reading. Turn off Wi-Fi before testing.
• Misreading the iPhone number. The field test shows a negative number; some people mistakenly think a higher absolute value is better. Remember: -70 is stronger than -100.
• Testing in one spot only. Signal varies by inches—moving a few feet can change the reading by 10 dBm. Walk around and take multiple readings for an accurate picture.
• Not checking the network type. The same dBm value means different things on 4G vs. 5G. A -100 dBm on 5G might be usable, while on 4G it’s poor. Note which network you’re on.

Tips

• Use the scale: Excellent: -50 to -70 dBm. Good: -70 to -85. Fair: -85 to -100. Poor: below -100 (dropped calls, slow data).
• Test at different times. Network congestion and weather affect signal. Check morning, midday, and evening to see the range.
• Test in different locations. Stand by a window, in the center of the room, and in the basement. This helps you find the best spot for calls or a Wi-Fi calling setup.
• On iPhone, you can keep the numeric readout permanently. After entering field test, force-touch (or long-press) the signal indicator and choose “Numeric” to keep it in the status bar. To revert, tap it again and choose “Bars.”
• For Android, use a third-party app if the built-in menu is hidden. Apps like “Network Signal Info” (free) show dBm and ASU without digging through settings. They read the same system data, so they’re accurate.

Troubleshooting

• The iPhone field test doesn’t open. Make sure you typed the code exactly: *3001#12345#*. If it still doesn’t work, update iOS; older versions had bugs. Alternatively, use the Settings > Cellular > Cellular Data Options > Voice & Data to see the network type, but not the dBm.
• Android doesn’t show signal strength in Settings. Some manufacturers (like Samsung) hide it. Try the dialer code *#*#4636#*#*. If that fails, install a third-party signal app from the Play Store—they read the same system information.
• The number keeps changing rapidly. That’s normal—signal fluctuates constantly. Take the average of three readings over 10 seconds.
• You see “No signal” or “-120 dBm” everywhere. This indicates a real coverage issue. Try resetting network settings (iPhone: Settings > General > Reset > Reset Network Settings; Android: Settings > System > Reset options > Reset Wi-Fi, mobile & Bluetooth). If that doesn’t help, contact your carrier—they may have a tower outage or your SIM may be faulty.
• The field test mode on iPhone shows a negative number but no ASU. That’s fine; iPhone only displays dBm. You don’t need ASU for practical purposes.

Frequently Asked Questions

What is a good cell signal strength number?

Generally, -50 to -70 dBm is excellent, -70 to -85 is good, -85 to -100 is fair, and anything below -100 is poor. The closer to 0, the stronger the signal.

Why does my phone show full bars but the dBm is -95?

Bars are a simplified representation—each bar covers a range of dBm values. A -95 dBm might still show 3 or 4 bars on some phones, especially if the network is LTE. Always trust the dBm number for accuracy.

Is there a way to improve my signal strength?

Yes. Move to a window, go to a higher floor, or step outside. If you’re in a building with thick walls, use Wi-Fi calling. A signal booster (repeater) can help at home, but check with your carrier for approved models.

Does 5G have different signal strength numbers?

The dBm scale is the same, but 5G can work at lower signal levels (e.g., -100 dBm) than 4G. However, 5G mmWave (high-band) drops off quickly with distance—you might see -80 dBm near a tower and -110 just a block away.

Can I test signal strength without a SIM card?

No, the cellular radio needs a SIM to connect to the network. Without a SIM, you’ll only see “No SIM” or emergency calls only.

Will these codes work on any phone?

The iPhone code works on all iPhones. The Android dialer code *#*#4636#*#* works on many Android devices (especially stock Android), but not all—Samsung, for example, often blocks it. The Settings method works on all Android phones, though the exact menu path varies.

Related

• How to Burn a CD/DVD in Windows 10
• Show Site Icons in Edge Favorites Bar
• Framework Laptop 12 Driver & Setup Troubleshooting Guide