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What is Signal-to-Noise Ratio and How to Measure it

Even with a strong WiFi router or mesh network, traffic can still be slow. The problem might not be the router, but all of the noise around it.
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We’ll help you understand what signal to noise means, and make your signal to noise ratio better to ensure steady traffic, smooth movie streaming, and quick downloads.

Signal to Noise: Separating Wheat from Tares

One of the most frustrating issues with accessing the Internet is when we set up the router, everything should be working right — and you move into the next room and the signal turns to garbage. Upgrade the router — and the signal still doesn’t seem to get any better. Upgrade to a fancy mesh network, only to find people in the conference room still aren’t able to hook their laptops into the WiFi even though the signal should be strong.

The problem may not be signal strength or the range of the network. It could be an issue with what’s called “signal to noise”, sometimes referred as SNR for short by people who feel that there aren’t enough acronyms in our life or people who giggle when they get us to say “snore” out loud when talking about WiFi.

SNR is a real issue, though. If your network should be working well but downloads or slow, or there are odd disconnects in certain locations in your building, investigating SNR to find out if that’s what’s plaguing your connections is well worth the time.

What does SNR Mean

Of course, the first thing when asking about how to fix “signal to noise ratio” issues is to delve into just what SNR means. Signal to Noise is a measurement of how much relevant WiFi signal there is compared to any other signals that can get in the way.

Usually, when dealing with WiFi issues, there are two main problems:

  • Dead spots: Places where our signal can’t reach. This can be because of distance to the WiFi router, the materials the building is made out of, and other related issues. With a dead spot, we just aren’t getting any signal at all.

  • Signal to Noise ratio: With signal to noise, the WiFi radio signals may be reaching just fine, but there are other radio signals that make it hard to pick out.

Think of each problem like a big room. If I’m on one side, and you’re on the other and you try to talk to me, if your voice is too soft I won’t be able to hear you unless you shout louder. That’s an issue with dead zones or signal strength.

Signal to noise is where we are in the same room, but the room is full of other people. As you try to talk to me, we have to complete with all of the noises other people are making. It doesn’t help if someone else has a voice similar to yours, so I have to figure out when it’s you talking versus someone else.

Understanding Signal-to-Noise Ratios

SNR isn’t a ratio, as in “there is 75% signal to 25% noise”, but is measured by taking the signal strength and subtracting the noise, not dividing it. Adding to the potential confusion is that the signal is measured in decibels. For those who work in audio, most people consider decibels a measure of sound as in how loud something is.

It gets worse. In WiFi, decibels are measured in negatives. If you remember old grade school math, negative numbers are the ones below 0. So if you have -15 dBm (deciBels per milliwatt), that is a stronger signal than -50 dBm. I know - it’s confusing, but once you get that the *higher* the number, the *weaker* the signal, the better off we’ll be.

Let’s take a look at two different rooms. In one, the average signal strength is -20, the noise is around -60. To get the signal to noise ratio, it’s the signal minus the noise, which means we have an average signal to noise of 40 in this case:

Signal to Noise Ratio
Signal to Noise Ratio

How about room 2, where the signal is also -20, but the noise is -25. Now our signal to noise is much lower — around 5:

Signal to Noise Ratio
Signal to Noise Ratio

Notice how difficult it is to tell the difference between the signal and noise lines on this chart compared to the first one? That’s the rule: the lower the signal to noise ratio, the worse communication will be. We want a nice, big number for our SNR or S/N ratio since that means there’s a lot of distance between our signal and our noise.

What is a Good Signal to Noise Ratio?

Remember that Signal to Noise ratio, sometimes referred to as S/N ratio, isn’t a “ratio” but the difference between the signal-to-noise. So the bigger the number, the better.

Most experts recommend that an SNR of 20 dB just for data — this is surfing the web, looking up charts and other related traffic. If you’re looking to stream high-quality videos or make good voice/video chats, then an SNR of 25 is going to be required. Here’s a list of what kind of Signal-to-Noise ratios to follow:

  • 5dB to 10 dB: Just give it up now. Stop what you’re doing, and fix the problems. The noise is so high that its indistinguishable from the signal.

  • 10 dB to 15 dB: Really slow, but at least there’s a signal. If all you’re doing is getting basic emails, then you can get by. Barely.

  • 15 dB to 25 dB: This is average and competent for web browsing and file downloading. Just don’t expect to be watching 1080p videos off Netflix and Youtube at a good rate.

  • 25 dB to 40 dB: Fast speed. This is where you can do video conferences, stream high-speed videos, and download large files like gigabyte sized .iso files or movies.

  • 40 dB and Up: You are in the Matrix, and have become the One.

Of course, this will be determined by your basic bandwidth strength. If your bandwidth strength is only -5 dB and your noise is 0, then your Signal to Noise is great but your signal strength is still trash. So first make sure the signal is strong, then focus on the signal to noise ratio.

How to Measure Signal vs Noise

One of the most useful tools that works as a signal to noise calculator comes from NetSpot.


The process is so easy, it’s just a few steps:

  1. Launch Netspot.
  2. Select Inspector.
  3. Select the WiFi network in question.
  4. Find the Signal and Noise levels.
NetSpot — network analyzer tool
NetSpot — network analyzer tool
  1. Subtract Signal minus Noise to get to the SNR.

Take our sample network. Here we have a signal of -39, and a noise of -80. So running this through our signal to noise calculator and we get (-39) - (-80) = 41. Or to save time, just look at the Level setting. If it’s green, the signal is clean.

Fixing SNR Issues

Fixing Signal to Noise issues can take a multitude of approaches. First, get a WiFi signal analyzer. We’ve already mentioned NetSpot, and that’s a great place to start. It shows a list of all of the networks it identifies.

NetSpot Inspector mode
NetSpot Inspector mode

Once you see the list of WiFi signals, you can do a few things to increase the SNR ratio:

  1. Remove Extra WiFi networks. This is especially true if this is a business environment. There are few reasons for someone to be running a separate WiFi network, whether it be from their cell phone and tethering or otherwise. With NetSpot, you can get an idea where it’s at as you trace it’s signal strength.

  2. Check for “Noisy” devices. Take a look at the devices around the WiFi router. Is it next to a television, refrigerator, or other electronic devices? Try moving it away a bit. There was once a place with awful WiFi coverage until someone discovered that the WiFi router was next to the company’s fire alarm bell. Once it was moved away, the signal noise dropped.

  3. Turn off unneeded signals. Some routers support multiple bands in the 2.4 GHz and 5 GHz range. Try turning off the 2.4 GHz signal if it’s not needed — it’s overcrowded compared to its 5 GHz sibling.

Wi-Fi Site Surveys, Analysis, Troubleshooting runs on a MacBook (macOS 10.12+) or any laptop (Windows 7/8/10/11) with a standard 802.11a/b/g/n/ac/ax wireless network adapter.
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These are just a few ideas, and there are more things to try on the Troubleshooting high noise level. But before you do anything, install Netspot. It has an excellent free version, and users who pay for the full version can get access to other amazing features like heat maps. Download and try it out to help resolve your signal to noise issues so you can use the fast Internet access you need.
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Read next in All about Wi-Fi

If you want to dive deeper into this Wi-Fi thing, check out the following articles about Wi-Fi security, the best apps for wireless networking, inflight WiFi, etc.
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Wi-Fi Site Surveys, Analysis, Troubleshooting runs on a MacBook (macOS 10.12+) or any laptop (Windows 7/8/10/11) with a standard 802.11a/b/g/n/ac/ax wireless network adapter.