About Network Calculator

CIDR subnet calculator with utilities. Part of the DevTools Surf developer suite. Browse more tools in the Networking collection.

Use Cases

• Calculate the usable IP range, network address, and broadcast address for any CIDR block.
• Plan IP addressing for a new office network with multiple VLANs.
• Determine if two IP addresses are on the same subnet given a mask.
• Find the smallest CIDR block that contains a given range of IP addresses.

Tips

• Enter CIDR notation (192.168.1.0/24) to get all derived values at once — network address, broadcast, first/last host, and total host count.
• Use the subnet divider to split a /24 into multiple smaller subnets for VLAN planning.
• Check the wildcard mask output when configuring Cisco ACLs — wildcard masks are the bitwise inverse of subnet masks and are required in access-list commands.

Fun Facts

• CIDR (Classless Inter-Domain Routing) was introduced in 1993 (RFC 1518/1519) to replace the Class A/B/C system, which had nearly exhausted IPv4's address space. CIDR allowed flexible prefix lengths instead of fixed 8/16/24-bit classes.
• IPv4 has approximately 4.3 billion addresses (2^32). The last unallocated /8 block was assigned by IANA to regional registries in February 2011. IPv6 has 340 undecillion addresses (2^128) — enough to assign 7×10^28 addresses to every person alive.
• The RFC 1918 private address ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) were allocated in 1996 as non-routable address space. NAT was invented specifically to allow these private addresses to share a single public IP.

FAQ

How many usable hosts are in a /24?

254 — the network address (first IP) and broadcast address (last IP) are reserved. For a /n subnet, usable hosts = 2^(32-n) - 2.

What's a wildcard mask?

The bitwise inverse of a subnet mask, used in Cisco ACLs and OSPF configurations. For a /24 (mask 255.255.255.0), the wildcard is 0.0.0.255.

Does it support IPv6?

Yes — enter an IPv6 prefix (2001:db8::/32) to get expanded notation, address count, and first/last address in the block.