How this is calculated

The /24 is ubiquitous because it's simple and fits the vast majority of home and small-office networks. With 254 usable addresses, you can connect every phone, laptop, smart TV, IoT device, and printer in a typical household with room to spare. In CIDR notation, /24 means the first 24 bits of the IP address are the network portion, leaving 8 bits for hosts (2^8 = 256). Moving to a /23 doubles your address space to 510 usable hosts; moving to a /25 halves it to 126.

Verdict

A /24 is the right default for any network with fewer than 200 devices. It's universally compatible, easy to reason about (the last octet is the host portion), and gives you headroom without being wasteful. If you're approaching 200 devices, step up to a /23 rather than adding a second /24 and dealing with inter-VLAN routing.