A higher dBm value means a stronger signal, so in most everyday situations, higher is better. If you’re checking your Wi-Fi or cellular signal strength, you’re almost certainly looking at a negative number like -65 dBm or -85 dBm. Because these values are negative, “higher” means closer to zero. A signal of -50 dBm is significantly stronger than -80 dBm, even though both numbers look small.
The confusion is understandable. The dBm scale is logarithmic and mostly lives in negative territory for the signals you encounter daily. Once you understand how the scale works, reading signal strength becomes intuitive.
How the dBm Scale Works
dBm stands for decibels relative to one milliwatt. The reference point, 0 dBm, equals exactly 1 milliwatt of power. Positive dBm values are stronger than 1 milliwatt, negative values are weaker. Most signals your phone or laptop picks up from a router or cell tower have traveled far enough that they’ve weakened well below 1 milliwatt, which is why you’ll almost always see a negative number.
The scale is logarithmic, not linear, so small numerical changes represent large real-world differences. Two rules make it easy to estimate:
- Every 3 dB doubles or halves the power. A signal at -40 dBm carries twice as much power as one at -43 dBm.
- Every 10 dB multiplies or divides the power by 10. A signal at -50 dBm is ten times stronger than one at -60 dBm, and one hundred times stronger than one at -70 dBm.
This means the gap between -60 and -80 dBm isn’t just “20 points worse.” It’s a hundredfold decrease in actual signal power.
Wi-Fi Signal Strength Ranges
Wi-Fi signal readings typically fall between -30 dBm (very strong, right next to the router) and -100 dBm (barely detectable). Here’s what different ranges mean in practice:
- -30 to -50 dBm: Excellent. You’re close to the access point and will get the fastest speeds your network supports.
- -50 to -65 dBm: Very good. More than enough for video streaming, video calls, and mobile devices.
- -65 to -70 dBm: Good. Reliable for web browsing, email, and most everyday tasks. Engineers recommend at least -65 dBm if you plan to use phones or tablets that move around a space.
- -70 to -80 dBm: Weak. Basic tasks still work, but streaming video or voice calls may stutter.
- -80 dBm and below: Unreliable. Connections drop frequently and speeds crawl.
Cellular Signal Strength Ranges
Cell phones measure signal strength using a metric called RSRP, reported in dBm. The same principle applies: closer to zero is stronger.
- -80 dBm or higher: Excellent. Premium signal with fast data and clear calls.
- -80 to -90 dBm: Good. Strong, reliable performance.
- -90 to -110 dBm: Fair to poor. You’ll notice slower data speeds, and calls may occasionally drop.
- Below -110 dBm: Deficient. The signal is unstable and you may lose connectivity entirely.
Bluetooth Follows the Same Pattern
Bluetooth devices transmit at power levels ranging from -20 dBm (0.01 milliwatts) up to +20 dBm (100 milliwatts). The receiver on the other end needs the incoming signal to be at least -70 to -82 dBm to maintain a connection, depending on the version of Bluetooth being used. Some newer low-energy implementations can pick up signals as faint as -103 dBm, which is why modern Bluetooth devices can maintain connections at surprisingly long distances.
Why Signal Strength Alone Isn’t Everything
A strong signal doesn’t guarantee a good connection. What really matters is how far your signal sits above the background noise, known as the signal-to-noise ratio (SNR). If your Wi-Fi signal reads -65 dBm and the noise floor in your environment is -90 dBm, your SNR is 25 dB, which is solid. But if you’re in a noisier environment where the noise floor is -80 dBm, that same -65 dBm signal only gives you 15 dB of SNR, and you’ll notice more lag and dropped packets.
For general data use, an SNR of at least 20 dB is recommended. Voice and video applications work best with 25 dB or more. So if your signal strength looks decent but performance is poor, noise is likely the culprit. Moving your router away from microwaves, cordless phones, and other electronics can lower the noise floor and improve your effective connection without changing the signal strength at all.
Can a Signal Be Too Strong?
In consumer situations, this almost never happens. But in radio engineering, feeding too strong a signal into a receiver causes saturation, where the electronics can’t process the input cleanly and the signal distorts. For specialized radio transceivers, this can occur when the input exceeds roughly 0 to +2.5 dBm. Consumer devices like phones, laptops, and routers have built-in protections that prevent this from being a real-world concern. For your Wi-Fi or cell signal, stronger is simply better.
Quick Reference for Reading dBm
Whenever you see a dBm reading on your phone, laptop, or router admin page, remember three things. The number is almost certainly negative. Closer to zero means stronger. And because the scale is logarithmic, a difference of 10 dBm means a tenfold change in power. If you’re troubleshooting a weak connection, aim to get your reading above -70 dBm for Wi-Fi or above -90 dBm for cellular, and you should have a stable, usable signal.