IPv4 subnet calculator
Enter an IPv4 address and CIDR prefix to see the network, broadcast, host range, mask and wildcard.
Runs 100% in your browserHow to calculate a subnet
- Enter an IP and prefix. Type a dotted-decimal IPv4 address and a CIDR prefix between /0 and /32.
- Read the breakdown. Network, broadcast, first/last host, mask, wildcard and host count update instantly.
- Copy or share. Use the Copy button to grab the summary block as text.
About IPv4 subnetting
Subnetting splits a network into smaller blocks so addresses are assigned where they are needed
and routing stays compact. A CIDR prefix like /24 says "the first 24 bits are the
network, the last 8 are hosts." The mask 255.255.255.0 encodes the same thing, and
the wildcard 0.0.0.255 is its inverse — useful in ACLs and OSPF where a 1
means "don't care about this bit." Usable host counts skip the network and broadcast addresses
in the normal case; /31 and /32 are the standard exceptions for
point-to-point links and host routes. This calculator runs entirely in your browser, so no IP
address you enter ever leaves the page.
Frequently asked questions
- It splits an IP address and CIDR prefix into the network and broadcast addresses, the usable host range, the subnet mask and wildcard, and the host count. Used to plan IP allocations and ACLs.
- Yes. All subnet math happens in your browser — nothing is sent to a server. The TrustChip above confirms the page makes no network calls.
- A /32 has a single host (a host route). A /31 is treated per RFC 3021 — both addresses are usable for a point-to-point link rather than reserved as network and broadcast.
- The bitwise NOT of the subnet mask. Used in ACLs and routing protocols (OSPF) where a 1-bit means "ignore this bit".
- The result lists the IP class (A–E) and whether the address falls inside the RFC 1918 private ranges 10/8, 172.16/12 or 192.168/16, plus loopback and link-local.