In the average nest, an eero device covers approximately 190m2 (the average UK home is a 2 bed terraced property with a floor area of 90m2).
That first eero placement is usually determined by where the fibre enters your home and you have access to power sockets. The general rule is the more central the better; the central point of your coverage is where the router is located.
To help you, here are some things to consider that may impact the location and/or number of additional node devices you may need to get whole home coverage:
Your home’s building construction (older with thick walls, or new builds with foil-insultation)
Your home’s layout
Wi-Fi interference from neighbour’s routers
Where you place your eero router (out in the open is better than behind the TV!)
There are some things you can do to optimise your Wi-Fi coverage though.
Something as simple as putting the eero on a table (off the floor) and somewhere clear of other devices that transmit a signal that may interfere with it will make a big difference.
If you're using additional eero nodes or eero Built-in devices, you can use the eero app to identify the best locations to place them, but the rules above should help you with some basic housekeeping ideas.