>>Hi,
>>
>>Currently I have the following router:
>>Linksys EA6900 wireless router. The problem with this router is that it does not well reach upstairs (the router is on the 1st floor). So, the computers/iPad on the second floor do not get a good receptions.
>>The online description of this router, EA 6900 AC 1900, does not show the area coverage.
>>Range extenders and wi-fi mesh networks provide a reasonable alternative in this scenario. The mesh network has a single ssid for the network so wandering around does not cause you any issue. Some extenders have additional ssid's which may mean reconnecting to that different ssid's as you move from area to area
>>
>>
>>pete
>
>Thank you, Pete.
>I ordered today a fairly expensive cable modem/router (made by Motorola). I will try it on Thursday/Friday.
>I wonder, if this router does not provide sufficient coverage, if I can buy the mesh extender for upstairs and see how it help.
>The Motorola router has a wider area it is supposed to cover (at least in the spec). So, I will see how it works.
>Again, thank you.

You've already bought a new device, and you should first test if it's good enough for your purposes.
For lurkers, a few comments:
- Any new Wi-Fi device you buy today should support at least Wi-Fi 6 (802.11ax, or "AX"). This is the successor to Wi-Fi 5 (802.11ac, or "AC"). The bleeding edge is tri-band Wi-Fi 6e but this is very new
- If you want to level up Wi-Fi from consumer equipment, a good option is Ubiquiti UniFi. One example access point (AP) is the U6-LR: https://www.amazon.com/Ubiquiti-Long-Range-Adapter-Included-U6-LR-US/dp/B08V1PF29L/ref=sr_1_1 . If you go UniFi there's some overhead in setting up the required infrastructure, I can give an overview if you're interested. I don't recall ever seeing any review that claimed a consumer Wi-Fi device was better than UniFi, but plenty that say UniFi is better
- A Wi-Fi mesh network can help in some circumstances but not all. If you can't get good performance anywhere upstairs, then a second AP upstairs would still have the same bottleneck back down to your main Wi-Fi so the performance anyone sees upstairs would not improve. However, if you can find a spot upstairs with good performance and put a mesh AP or extender there, client devices upstairs may work better
- Another option to get through areas that block Wi-Fi is a powerline ethernet adapter kit such as https://www.amazon.com/TP-Link-Powerline-Extender-TL-WPA8631P-KIT/dp/B08RHZBHTM/ref=sr_1_8 . This creates a link to a new AP upstairs through your electrical cabling, which can be faster than Wi-Fi to the same spot
- Similar to the above, if you have coaxial cabling between downstairs and upstairs you might be able to use a MoCA kit such as https://www.amazon.com/Hitron-Ethernet-existing-Backbone-Streaming/dp/B08MQG6T61/ref=sr_1_2_sspa . I haven't used any myself but they promise considerably higher performance than powerline extenders
- Of course, if you can run one Cat6 Ethernet cable upstairs and set up another AP, all your problems are solved ;)

One real-world data point: I have one client with their internet service (300Mbps down) in their basement. One user is 2 floors above that. Each floor is concrete with wire mesh reinforcement and in-floor radiant heating via copper tubing. A few years back I set them up with a UniFi Wi-Fi 5 LR AP. Upstairs this gives them 40 - 50Mbps down on an Ookla speedtest.
They wanted more so I set them up with a pair of 1st generation TP-Link powerline adapters. This gives 80 - 90Mbps down. However, these adapters seem to freeze 3 or 4 times a year and need to be manually power cycled. The UniFi AP has been rock solid.
I don't know how much improvement they would see with a Wi-Fi 6 AP or the latest generation powerline adapters.
For reference, a "full HD" 1080p video stream consumes ~13-15Mbps.