Subnet & CIDR Calculator
Whether you need a fixed IP for your server or a subnet for Docker, this tells you the network, broadcast and usable range in one go.
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Use it to pick a safe static IP for your server (stay outside your router's DHCP pool) or to work out what a Docker network like 172.17.0.0/16 actually covers. Prefixes /31 and /32 are special-cased: they have no separate network and broadcast addresses.
Where subnet maths actually shows up at home
The most common job is picking a safe static IP for your server or Pi-hole: routers usually hand out DHCP leases from .100 upward, so a fixed address like192.168.1.10/24 keeps you out of the way. The second most common is Docker: the default bridge network is 172.17.0.0/16, and when you create custom networks their ranges can collide with a VPN tunnel if you are not deliberate about it.
A home LAN is almost always a /24 — 254 usable addresses, room for well over a hundred devices — while a /30 is the classic point-to-point link between two routers. If you are juggling multiple homes, extra subnets or VLANs, the Tailscale and local DNS guides below are the natural next reads.