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I presented at two events last week (totally separate topics) and the same two questions came up at both – how many users can I put on 1 AP and does 11ac change this?
If you have ever attended one of my presentation you will have head this – ‘It Depends’.
This is always true and will continue to be so no matter if you are doing 11a, 11n, 11ac, or whatever comes next. My normal answer to this question is to turn it around and get feedback from the audience on what number they think is correct, I get a wide variety of answers and then explain they are all correct, because it really does depend. It depends on the client devices, it depends on the applications and most importantly it depends on the expected and/or required user experience demanded by the users.
As noted, I work for Xirrus, on our products we can support 120 or 240 associations per radio and as a result this means up to almost 4000 association can be supported on our largest products. Would you ever design a solution based on those numbers? No, this is because that what you can do is not always what you should do. In example – I can probably transport 20 students in the back of a pickup, but not really something you would do
It all comes down to what is the expected or designed user experience and I like to use K-12 schools to demonstrate as they make a great example. If I need to provide Wi-Fi for elearning in the classroom, I will design for about 20 users per radio to provide a reliable ‘wired-like’ experience. Now if coverage was also desired in the cafeteria I would design for 20-40 per radio as normally the level of service is not are stringent. And finally for the sports stadium I might design with even higher densities, once again it depends on the level of service I want to provide to the end user.
Bottom line there is no magic number, different devices with different capabilities, connected at different data rates and requiring access to different applications will have a greater impact on network performance, see graphic below and you will start to appreciate the impact of the client types.
As an example, if I have a clients connected at 300 Mbps and on the same radio I have other clients connected as low as 6Mbps the overall performance is degraded because even though both get their max data rate ‘when they have the air’, it will take the slower client 50x as long to send the same packet and the other clients will have to wait their turn. And in most environments clients will not be connected at the max date rates available.
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The Wi-Fi Professor: Perry Correll 
You end on a very valid point there; many capacity planning exercises do the sums with all clients profiled using the highest possible data rate….which I’ve certainly never seen in the real world! 🙂
Comment by Jon Foster June 12, 2014 @ 3:22 pm