WiFi’s Hidden Speed Limits

I hear it off and on and have experienced it myself more times than can be recounted: “My WiFi is too slow!”. Some people blame it on their internet service provider, and while internet service may be the sole culprit in slow WiFi performance, more often than not, in my experience, it’s either some other factor at play or a combination of factors that can seem to cripple WiFi speeds.

Now, to get this out of the way: WiFi is not “the internet”. Your router’s WiFi is a conduit for your local and internet communications. To muddy the waters here a little bit, WISPs (wireless internet service providers) generally use WiFi technology for their customers and is subject to the same hidden speed limits that I’m speaking about here. This limitation shouldn’t exist with wired internet (cable, fiber, DSL), but I’ve seen similar behavior personally in poorly-managed cable internet networks, so I assume it could happen elsewhere in cable systems and with DSL internet if using old copper wiring still. This is mostly speculative outside of my few personal experiences, but this post is really about wireless networks: WiFi and wireless internet connections.

Before we can get into this obscure and widely-unknown WiFi limitation, we should cover another WiFi limitation that most people do not know about. It’s more of a misunderstanding of marketing terms vs real potential performance, but can factor into the speeds you actually see over WiFi.

Wireless connection rate vs real speed

Usually with a wireless device, you can see what is called a connection rate. It may be called ‘link rate’, ‘wireless rate’, etc, depending on the device. Your WiFi’s connection rate is not the actual speed you’ll see over WiFi. Rather, it’s a representation of the maximum theoretical speed of a wireless connection at the moment. Here are a couple of examples.

Here’s a connection rate for a 5Ghz mobile device to a local router:

Here’s a speed test with that device. The upload speed is a limitation of the WiFi, the download speed limit is due to network use at the time of the test:

5Ghz WiFi speed test on a mobile device

You can see that even though the connection rate is 390Mbps, the max speed is about 80Mbps over WiFi.

With a 2.4Ghz device, the differences are even more obvious:

2.4Ghz WiFi connection rate vs speed screenshot

Using the same speed test site to the same server in the same network, I only saw speeds of around 20Mbps over WiFi despite a WiFi connection rate of over 100Mbps, and an internet connection that will do about 60Mbps x 120Mbps at the time of testing.

You see marketing for 300Mbps, 600Mbps or even 1.3Gbps WiFi advertised on routers. This is misleading at best and not representative of the actual speeds your router’s WiFi can deliver to a device. The reasons for that are largely outside the scope of this article, but for some more info on this, I recommend browsing through these:

They are more technical in nature, but I think can be useful.

Wireless and per-connection limits

Generally speaking and for the purposes of this article, wireless connections have two types of speed limits: a saturated, “max capacity” speed and a per-connection speed. Under ideal conditions, these speeds tend to be similar. However, if you’re using WiFi in a populated area, especially 2.4Ghz WiFi, or have a less-than-ideal connection to your router for any reason, this is where you can run into these limits.

To get this out of the way, these per-connection limits won’t affect you as much when you’re browsing the web on a wireless device. Web pages today are made up of dozens to hundreds of small or tiny “elements”, all of which must be downloaded to your device before the page will finish loading. Modern web browsers like Firefox, Chrome and Edge allow up to 6 connections at a time by default, so each web page you visit will download each of those background elements, up to six at a time, one after another, until the web page fully loads. If you’re seeing speed instability on a per-connection basis you’ll likely see some lag in loading web pages, but being able to use multiple connections can make the experience less unpleasant.

Contrast that to say, for instance, downloading a file with your web browser or even potentially streaming video over WiFi. In these cases, you will not likely have the benefit of downloading using multiple connections. Instead, you’ll have one connection, usually, pulling all of the data. This is where you’ll see the biggest impact from this largely unknown WiFi limitation.

Per-connection limit speed test example

I ran a brief test to demonstrate what I mean by per-connection limit. I had a laptop plugged into a router via LAN port and my phone connected to the 2.4Ghz WiFi option. From about 15′ away through a wall, I had “3 bars” on my phone, which I believe was around -65. Realistically, that’s pretty good signal. I ran two Iperf tests: one that looked at speeds for one connection at a time (one item downloaded at a time until completed), then speeds for 7 connections at the same time.

Here’s the one-at-a-time result:

Iperf single connection speed test result

Under the Bandwidth column, you can see the speeds: 1Mbps-5Mbps, outside of the one test run that didn’t complete. Whether you’re downloading a large file or streaming a video, the WiFi performance in these conditions will behave just like this: 1Mbps one second, 3Mbps the next, sometimes you may stop passing traffic for a second, etc. This is 2.4Ghz WiFi. 5Ghz WiFi that is heavily affected by local interference or has poor signal or connectivity due to obstacles seems to behave similarly, though the speeds are faster, where you might see up to 6Mbps-8Mbps even with a poor connection. At least with 2.4Ghz, I’ve seen this behavior countless times on home routers and outdoor wireless equipment alike, testing every which way from Tuesday.

Here are the speed test results from 7 simultaneous connections:

7 connection iperf speed test over WiFi screenshot

You can see that with this test, taken just a moment later from the same location, I was able to pull 10Mbps over the WiFi, at least when taken as a whole. Now, I could run these tests over and over and get somewhat different results, but the bigger-picture point remains the same: in real-world scenarios, you can easily run into these hidden WiFi limits, even if you have fairly good or even good WiFi signal.

WiFi and its hidden speed limits

WiFi isn’t the same as wired. WiFi has limitations that fluctuate based on the time of the day and location of your device relative to your router or wireless AP. Just because you have a 100Mbps internet connection doesn’t inherently mean you’ll see 100Mbps speed to any wireless device, and depending on numerous factors, some of which are outside of your control and your ISP’s control, it’s possible that you may only see a fraction of that, even if your WiFi connection can technically handle more.

I plan to write up an article on how to improve your WiFi’s performance, but the best way to minimize being affected by this is to use a dual-band router, and opt to use the 5Ghz band if your device will support it.

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