Satellite signals are measured in dBm. But what’s a dBm?

The more time you spend in the world of satellite TV, the more you realize it’s pretty daunting. Sure, watching TV is easy. Using the equipment once it’s installed is actually pretty simple. However, the installation aspect was definitely not designed for the average joe. And let’s be honest, it’s actually gotten harder to understand since the 1990s.

When DIRECTV launched in 1994, the average person could put up a dish and a couple hours later be watching satellite TV. They’d have to do it themselves, because there were no professional installers back then. Today, practically every new satellite TV system is professionally installed. Then again, the average satellite customer doesn’t come to Solid Signal. We’re here for you folks who really want it your way. And I’m here to explain how you can tell what your satellite signal strength is.

dBm. What is it and why do I care?

Satellite signals are measured in dBm as the title of this article says. But you’ve probably never heard of dBm before. You’ve heard of volts, watts, stuff like that, but dBm looks like some sort of mistake. Who puts a big B in the middle of an abbreviation? Let’s dig deeper.

How electrical terms are named

Every electrical term you’ve ever heard is named for a pioneer in the field of electricity. James Watt, Alessandro Volta, Heinrich Hertz, André-Marie Ampère, Georg Ohm and more are immortalized in measurements that bear their names. So too is Alexander Graham Bell, the man who (might not have) invented the telephone and (definitely) brought telephone service to the world. The bel is named for him.

What is a bel?

A bel is a measure of “how much more.” If you have 1 bel more of anything, you have ten times more. It doesn’t matter if it’s electricity, sound, or breakfast cereal. If you have one quarter today and tomorrow you have two and a half bucks, you have gained one bel of quarters.

In order to make it easier to use bels as a measurement, they are usually divided in 10. Remember when your 5th grade teacher tried to teach you about the metric system and you thought you’d never need it? Sorry, you owe Mr. Price an apology. A decibel is 1/10th of a bel, and represents the steps between “what you have” and “10x what you have.” It’s logarithmic which is a whole concept I don’t have time to explain. Just know that three decibels is roughly twice as much, six decibels is roughly four times as much, and ten decibels — one bel — is ten times as much.

This keeps working on and on. 20 decibels is one hundred times as much, 100 decibels is 10,000,000,000 times as much. Every time you add 10 decibels, you multiply by 10. It’s very handy for expressing large changes with small numbers.

Amounts less than what you have are expressed with negative decibels. -10 decibels is one-tenth as much. -20 is one one-hundredth as much, and so on.

We abbreviate bels as B, so we abbreviate decibels as dB.

What about the “m” in dBm?

So assuming you’re still with me, you know that decibels is a relative level. It has to be relative to something. In the case of dBm, you’re comparing the number to one milliwatt, or 1/1000 of a watt.

A watt is a measure of signal power that combines two other measurements, volts and amps, to try to give you a good idea exactly how much electricity is being used. Signals that get to your satellite dish are very, very weak and are expressed in fractions of a milliwatt.

In fact, the signal that gets to your satellite receiver is usually about -50dBm. Looking at that, we know that -50 describes a fraction 1/100,000. Start with a milliwatt, and that means the signal is…

.00000001 watts. That’s a seriously weak signal.

Pretty impressive that you can get 1,000 channels of digital TV from a signal that’s got so many zeros in it. If I read that number right, it’s one-ten-millionth of a watt.

Because the numbers are so small, using dBm instead of watts makes it easier to talk about the signal we have and the signal we need. The signal coming out of your satellite dish’s multiswitch is going to be about -25dBm. It loses 25dBm, or something about 99.3% of its strength, by the time it gets to your receiver.

How to use dBm in your everyday life

OK you probably won’t use dBm in your everyday life. But you’ll use it when you’re making sure you have good satellite signal. With such a weak signal to work with, it’s important that you keep it as strong as possible. Every foot of cable, every connector and every splitter cuts down that signal level. Keeping your system simple means keeping as much signal as possible, and with so little to start with, that’s important.

If you’re looking for the best accesories and tools to simplify your satellite system, check out the great selection at

About the Author

Stuart Sweet
Stuart Sweet is the editor-in-chief of The Solid Signal Blog and a "master plumber" at Signal Group, LLC. He is the author of over 8,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.