does number of devices connected to WiFi affect speed

A properly designed wifi system can manage a large number of devices.  A device that is off but previously connected won’t affect performance of the router.  

gr8sho, thank you for your response. A  couple of follow up questions:

1. Can I assume, if I am having AT&T providing a new gateway system, it will be " a properly designed wifi system" able to handle multiple devices?

2. Is there a performance relationship between TV and internet if I get DirecTV off a satellite dish and internet via WiFi?

Thanks

There are only four gateways, depending on your type of service, and they would be configured for their intended purpose / usage. 

DirecTv Satellite service only uses the internet for video on demand, streaming…. Standard programming would come from the dish. 

Types on internet service…

* fiber/copper hybrid (FTTN or ADSL2+) previously known as Uverse would receive the BGW-210 gateway

* direct fiber FTTP speeds of 300 or greater should receive BGW-320 but may receive BGW-210 with external ONT

* G.Fast for selected multi dwelling units (apartment/condo) receive the Rokus(?)

* ATT AIR, FWA product receives the CGW-450 ALL FI HUB

Note… in all cases there is a total bandwidth received by the gateway that is distributed to the devices… the more devices in use the lower the overall bandwidth accessible.

An example is internet 25, HD usage on a device is around 5.5 to 6 thus a maximum of (4) devices could be consuming HD streams without affecting performance… the faster the speed profile the more active devices that could exist at any point in time.

edit… how many devices in HD for folllowing internet plans… 10… 50… 100… 300… 500.

4K uses from 15 to 25 per stream while SD (stand definition) is around 1.5 to 2 per stream.

@jsias4125  Keep in mind that AT&T gateways, at least as posted here, do not have very robust WiFi systems. Especially if you have quite a few device that use both radios (2.4GHz and 5GHz). Folks who have had issue have resorted to purchasing their own router/WiFi system and either set it up as access points or, better yet, set it up as a mesh WiFi system by disabling the WiFi in the gateway. So, if you have issues with WiFi coverage or reliability, that may be an option. You could try extenders but they don't seem to work very well either. Of course, it all depends in a large part on how big of an area you need to cover (square footage, one-story, two-story, from the basement, etc), the number of wired/WiFi devices connected at any one time, etc. All you can do is get the gateway installed and see how it goes. You do have options if WiFi coverage becomes an issue. Wired, when possible, is always better than WiFi for speed and reliability.

Can someone talk about wired vs. WiFi. I currently use WiFi with a booster/extender inline all in one room on the first floor. 

I have a  2100 square foot home, no basement

all we have is two cell phones and two laptops connected at 40 mbps which has been tolerable but I can now double my mbps at no additional cost thru my current provider (Century Link). The phones are powered on all the time (though asleep when not in use) and the laptops are completely turned off at night

95% of our usage in on the first floor - the other 5% is upstairs with a cell phone and a laptop for book reading (off line)

          How extensive would the wiring be - would it need to include the second floor and what kind of cost would be entailed

          We  do no gaming or streaming on any of our devices - in my situation, is the "speed and reliability" gain of wired worth the effort and hassle?

Finally - and I do appreciate the level of effort in responding to my many question - AT&T's Internet Air web page states,

Typical Download Speed

75-225 Mbps WHAT CAN I EXPECT?" 

Well, there's a whole heck of a lot of difference between 75 and 225 mbps. How can I determine what I will get for speed?

Thanks,

Jon

@jsias4125  If your current setup works ok for now, then continue to use it with the new gateway unless you develop issues, then consider your alternatives. It may work just fine and you're good to go. I would not use the extenders that AT&T sells because they aren't that good and they charge you $10 per month. Or at least they used to.  I don't use AT&T as my ISP so it may be different now.

Wiring your extenders or satellites back to the router with ethernet affords a much more reliable connection. Simply because the connection is not hindered by any of the issues that plagues WiFi in general (distance, walls, construction materials, etc). The connection speeds are typically a bit faster than WiFi for the same reasons. Given the number of devices you have connected you shouldn't have any issues with overtaxing your system.

If you don't need to use Internet Air, which is a fixed wireless internet (5G) connection, then don't. It's only available in areas that don't offer a cable/fiber internet connection. Keep in mind that all speeds, regardless of how you get your service, are "up to". 225Mbps, for example, is the maximum you could get but in reality, it may be less for lots of reasons. If you don't stream anything or game, then 100Mbps download would probably be sufficient.

@jsias4125 

No supported gateway provided by Att has acceptable WiFi IMO.  As to what comes next? Well there’s always a first time.  
Now that sounds bad I know, but you can look at as glass half full and adding your own chosen WiFi system isn’t a terrible solution considering all the alternatives.  

Now about this point of number of phones and laptops, those numbers just aren’t a concern.  

Some observations…

* have CenturyLink as hardwired DSL, means your in the western half of the US as the eastern half of US was sold to BrightSpeed.

* CenturyLink and ATT would not be offering hardwired service at same address, thus looking at ATT AIR, a Fixed  Wireless Access product similar to the 5G FWA offerings from T-Mobile and Verizon were available.

* speeds can and will vary based upon proximity to tower, line of sight and possible interferences including capacity at the tower which varies based upon time of day and those connected to the tower at any given time. 

* self install with reasonable cost and unlimited data.

* 14 day trial period, cancel within 10 days if not going to work for your needs. 

some cons include this is CGNAT meaning receive a private IP address from a pool of addresses from upstream device, this can affect certain services that use geo location such as Hulu and local sites as may be listed as being elesewhere. 

ATT and DirecTV used to be married, now they're just good friends. I'm considering Internet Air as an ISP for internet TV from Direct TV. Any thoughts on things such as outages on DirecTV's internet TV?   What about signal quality of satellite vs. internet TV signals? 

Internet Air is AT&T's wireless 5G cellular offering. It is wireless so just be aware of the shortcomings of wireless technology for internet/DTV access. It does work, but.....