dBm (decibel-milliwatts) is a unit that measures signal power on a logarithmic scale, where 0 dBm equals exactly one milliwatt of power. In practical terms, it’s the most reliable way to know how strong your Wi-Fi or cellular signal actually is. Unlike the signal bars on your phone, which vary by manufacturer and carrier, dBm gives you a standardized number you can compare across any device or network.
Why Signal Strength Uses a Logarithmic Scale
Radio signals span an enormous range of power levels, from billionths of a milliwatt at your phone’s antenna to thousands of milliwatts at a cell tower. Expressing all of that on a simple linear scale would mean comparing numbers like 0.000001 mW to 1,000 mW. The logarithmic dBm scale compresses this range into manageable numbers, typically between -120 and 0 for the signals your devices receive.
Two rules make the scale intuitive once you learn them. Every 3 dBm increase means the power has doubled. Every 10 dBm increase means the power has multiplied by ten. So a signal at -50 dBm carries ten times more power than one at -60 dBm, and roughly a hundred times more than one at -70 dBm. This also works in reverse: dropping from -60 to -63 dBm means you’ve lost half your signal power.
Because the numbers are negative (your device receives far less than one milliwatt), higher values are better. A signal at -45 dBm is much stronger than one at -85 dBm.
What the Numbers Mean for Wi-Fi
Wi-Fi signal quality falls into fairly well-established ranges. At -30 dBm, you’re essentially standing next to the router, and that’s about the strongest reading you’ll see in normal use. At -50 dBm, the signal is excellent. At -60 dBm, it’s very good, and you’ll still see full bars on most devices. Around -65 dBm is where reliable performance starts to taper, though connections remain solid.
For stable connections, especially video calls, streaming, or file transfers, you generally need -70 dBm or better. A reading of -65 dBm or stronger is recommended for latency-sensitive tasks like video conferencing or online gaming. Once you drop below -70 dBm, you’ll start noticing slower speeds, buffering, and occasional disconnects. Below -80 dBm, the connection becomes unreliable for most purposes.
Cellular Signal Ranges
Cellular networks use a different set of thresholds because the signals travel much farther and pass through more obstacles. The key measurement for LTE and 5G is called RSRP (Reference Signal Received Power), and it’s reported in dBm.
- -80 dBm or higher: Excellent. Premium signal strength with fast data speeds and reliable calls.
- -80 to -90 dBm: Good. Strong enough for HD streaming, video calls, and consistent performance.
- -90 to -110 dBm: Fair to poor. Speeds slow noticeably, and you may experience dropped calls or failed downloads in the lower end of this range.
- -110 dBm or weaker: Deficient. Signals are unstable, and maintaining a connection becomes difficult.
These ranges are wider than Wi-Fi because cell towers serve users across miles, not feet. A reading of -95 dBm on a cellular network is workable, while that same number on Wi-Fi would indicate a serious problem.
Why Signal Bars Are Unreliable
The bars on your phone are a rough translation of dBm into a visual indicator, but every carrier and phone manufacturer uses its own algorithm to decide how many bars to display. One phone might show three bars at -90 dBm while another shows one bar at the same strength. There’s no universal standard. This makes bars useful for quick glances but unreliable for diagnosing actual connectivity problems. If you’re troubleshooting a weak signal or comparing coverage in different spots, dBm is the number you want.
Signal-to-Noise Ratio Matters Too
A strong signal doesn’t guarantee a good connection if there’s too much background interference. Every wireless environment has a noise floor, the baseline level of electromagnetic interference from other devices, neighboring networks, and electronics. Your usable signal quality depends on the gap between your signal and that noise floor, known as the signal-to-noise ratio (SNR).
If your device picks up a Wi-Fi signal at -65 dBm and the noise floor sits at -80 dBm, the SNR is 15 dB. That’s enough for a basic connection but not a great one. An SNR of 25 to 40 dB is considered good, while anything above 40 dB is excellent. Below 10 dB, the signal is nearly indistinguishable from noise, and establishing a connection becomes almost impossible. This is why moving your router away from microwaves, baby monitors, and clusters of Bluetooth devices can improve performance even when the dBm reading stays the same.
How to Check dBm on Your Phone
Android
Turn off Wi-Fi first if you want to measure cellular signal. Go to Settings, then About Phone, then Status Information or Network (the exact wording varies by manufacturer). Tap SIM Card Status, and look for Signal Strength. Your dBm reading will be listed there, usually as a negative number next to “dBm.”
iPhone
Apple buries this information in a diagnostic screen called Field Test Mode. Turn off Wi-Fi, open the Phone app, and dial *3001#12345#* then tap call. Field Test Mode will open with a set of technical readouts. Look for the RSRP value, which is your signal strength in dBm. Apple changes the layout of this screen between iOS versions, so the exact location of the RSRP reading may shift, but it’s always somewhere within this mode.
For Wi-Fi dBm readings, most phones don’t display the number natively. On Android, free apps like Wi-Fi Analyzer will show you the dBm of every nearby network. On Mac or Windows laptops, built-in network diagnostics tools can display Wi-Fi signal strength in dBm as well.
Putting dBm to Practical Use
Knowing your dBm reading turns vague complaints like “my internet is slow” into actionable information. If your Wi-Fi reads -72 dBm in your home office, you know the signal is borderline and that moving your router closer, adding a mesh node, or switching to a wired connection would help. If your cellular signal reads -105 dBm at your desk, you know you’re in poor coverage territory and a window seat or signal booster could make a real difference.
Walk through your home or office while watching the dBm reading and you’ll quickly map out where coverage is strong and where it drops. The number changes in real time, and because it’s standardized, the reading means the same thing regardless of what device you’re holding or which carrier you use.