How many switches do I need for 27 computers?

to be honest if you need to ask you are out of your depth

The depends, it could be one 32 port switch, or 2 16 port, etc.

One 48 port or 96 port switch will do it all, and have spare ports fro expansion.
If using 5 port home switches, you would likely need 7 of them, as one port on each switch would be used to connect/chain to another switch, leaving about 28 ports for computers (give or take one or two)

How many ports in the individual switch? Easiest would be one enterprise grade switch to cover to all, but it is not very hard to work it out.

Depends on the switch.

Commercial switches I've seen often are available in 32 port models; you'd only need one of those.

If you're doing something with "consumer-grade" equipment... I might suggest four 8-port switches, and one 4-port switch. (Your router probably has a 4-port switch, built-in.) That would support 28 computers.

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