Signal strength is a measure of how much power a wireless signal has when it reaches your device. Whether you’re talking about cell service or Wi-Fi, stronger signals mean faster data speeds, clearer calls, and more reliable connections. The most accurate way to express signal strength is in decibel-milliwatts (dBm), a scale that typically runs from -50 dBm (excellent) to -120 dBm (virtually no connection).
How Signal Strength Is Measured
Two units come up most often: dBm and RSSI. They both describe the same thing, but they work differently. dBm is an absolute measurement of power on a logarithmic scale, meaning each small change in number represents a large change in actual signal power. The closer the value is to 0, the stronger the signal. A reading of -55 dBm is significantly stronger than -85 dBm, even though the numbers don’t look that far apart.
RSSI, or Received Signal Strength Indicator, is a relative index. The Wi-Fi standard allows RSSI to sit on a scale of 0 to 255, but each chipset manufacturer defines its own maximum. Cisco uses a 0 to 100 scale, while Atheros uses 0 to 60. Because there’s no single standard, RSSI readings from one device aren’t directly comparable to readings from another. That’s why most professional tools report signal strength in dBm instead.
What the Numbers Mean for Cell Service
Your phone’s signal bars are a rough visual shorthand, but dBm gives you the real picture. Here’s what different ranges feel like in practice for 4G LTE and 5G connections:
- -50 to -79 dBm (4 to 5 bars): Excellent. Calls are crystal clear, and data speeds are at their peak.
- -80 to -89 dBm (3 to 4 bars): Good. Reliable service with steady data speeds for streaming, video calls, and downloads.
- -90 to -109 dBm (2 to 3 bars): Fair. Data slows noticeably, though calls still work. You may see buffering on video or delays loading pages.
- -110 to -120 dBm (0 to 1 bar): Poor. Spotty to no service. Calls drop frequently, and data may not function at all.
Most phones let you view your exact dBm reading in the settings. On iPhones, it’s buried in the Field Test mode. On Android devices, you can usually find it under Settings > About Phone > SIM Status or Network.
Why Your Signal Bars Can’t Be Trusted
There is no industry standard that dictates how many bars correspond to a given signal level. Each phone manufacturer uses its own formula. Two different phones sitting side by side on the same cellular network can show different bar counts even when their underlying dBm readings are nearly identical. One phone might show three bars at -88 dBm while another shows four.
This makes bars useful for spotting general trends (moving from one bar to four means things improved), but unreliable for comparing devices or diagnosing connection problems. If you’re troubleshooting poor service, checking the actual dBm value is the only way to know what’s really happening.
Wi-Fi Signal Strength Thresholds
Wi-Fi follows the same dBm scale, but the practical cutoffs differ slightly because Wi-Fi operates over shorter distances with different hardware. A good rule of thumb: if your Wi-Fi signal reads weaker than -70 dBm, you’re unlikely to get good performance for bandwidth-heavy tasks like 4K streaming, video conferencing, or large file transfers. Basic browsing and email can tolerate weaker signals, but anything demanding real-time data transfer needs that -70 dBm floor or better.
Walls, floors, metal appliances, and distance from the router all weaken Wi-Fi signals. A signal that reads -45 dBm in the same room as your router might drop to -75 dBm two rooms away, especially if there’s concrete or brick in between.
The Logarithmic Scale Makes Small Numbers Deceptive
Because dBm is logarithmic rather than linear, the numbers behave in ways that aren’t intuitive. Every 3 dB of gain doubles your actual signal power. So a jump from -80 dBm to -77 dBm doesn’t sound like much, but it means your device is receiving twice the power it was before. Conversely, dropping from -70 to -73 dBm cuts your signal power in half. This is why even small improvements in positioning or equipment can have outsized effects on your connection quality.
How to Improve a Weak Signal
If your dBm readings land in the fair or poor range, you have a few practical options depending on whether the problem is cellular or Wi-Fi.
For cellular signals, a signal booster (sometimes called a cell booster or amplifier) uses an external antenna to capture a stronger signal from the nearest tower, amplifies it, and rebroadcasts it inside your home, office, or vehicle. Boosters work in both directions, strengthening the signal your phone sends back to the tower as well. The external antenna matters: a directional antenna aimed at a specific tower pulls in more signal but covers a narrow angle, while an omnidirectional antenna captures from all directions at lower strength. If you know where your nearest tower is and have a clear line of sight, a directional antenna paired with a booster delivers the best results. In hilly or mountainous terrain, a lower-gain antenna with a wider spread often performs better because the signal is less likely to be blocked.
For Wi-Fi, the simplest fix is moving your router to a central location, elevated off the floor, and away from metal objects or thick walls. If your home is large or has difficult construction materials, a mesh Wi-Fi system places multiple access points throughout the space so you’re never far from a strong signal. Switching your router’s frequency band can also help: 5 GHz delivers faster speeds at shorter range, while 2.4 GHz travels farther through walls at slower speeds.