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Subnet Calculator

Type an address with a prefix, like 192.168.10.25/24 or 2001:db8::/48, to get the full breakdown, subnet splits and ready-to-paste config.

Details

Binary

Network bitsHost bits

Config snippets

replace the interface name

Split into smaller subnets

Subnet size

Keep an eye on every host in that range.

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IPv4 CIDR cheat sheet

PrefixNetmaskWildcardAddressesUsable hosts

How subnetting works

An IPv4 address is 32 bits. The prefix length (the number after the slash) says how many of those bits identify the network; the rest identify hosts inside it. In a /24, the first 24 bits are the network and the last 8 bits leave 256 addresses. The first address is the network address and the last is the broadcast address, which leaves 254 usable hosts.

/31 networks (RFC 3021) are a special case for point-to-point links: both addresses are usable and there is no broadcast address. A /32 is a single host, often used for loopbacks and routes. Private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are not routed on the internet. 100.64.0.0/10 is the carrier-grade NAT range ISPs use between customers and their NAT.