Free CIDR / Subnet Calculator
Compute the network address, broadcast, usable host range, subnet mask, and wildcard mask for any IPv4 or IPv6 CIDR block. Split a parent network into smaller equal-size subnets and see whether the address falls in a private, loopback, link-local, multicast, or reserved range under the relevant RFC.
Split into smaller subnets
4 subnets| # | Network | Broadcast |
|---|---|---|
| 1 | 192.168.1.0/26 | 192.168.1.63 |
| 2 | 192.168.1.64/26 | 192.168.1.127 |
| 3 | 192.168.1.128/26 | 192.168.1.191 |
| 4 | 192.168.1.192/26 | 192.168.1.255 |
How to use
- 01Pick IPv4 or IPv6.
- 02Type a CIDR like 10.0.0.0/8 or 2001:db8::/32. The result updates as you type.
- 03Read the network address, broadcast, first and last usable host, mask in dotted form, and the wildcard.
- 04For IPv4, optionally split the parent into subnets of a smaller prefix to plan VLAN allocation or VPC subnet design.
- 05Click "Copy report" to paste the result into a ticket or design doc.
FAQ
What is CIDR?▼
Classless Inter-Domain Routing notation. A network is written as IP/prefix where prefix is the number of leading bits that identify the network. 192.168.1.0/24 means the first 24 bits are network bits and the remaining 8 bits identify hosts.
Why are first host and last host different from network and broadcast?▼
In any IPv4 subnet larger than /31, the network address (all host bits zero) and broadcast address (all host bits one) cannot be assigned to a host. The usable range is everything between them. For /31 and /32 there is no broadcast address, so all addresses are usable.
What does the wildcard mask mean?▼
A wildcard mask is the bitwise inverse of the subnet mask. Cisco access-control lists historically expect masks in this form. /24 has subnet mask 255.255.255.0 and wildcard 0.0.0.255.
How do private and reserved ranges work?▼
Several IPv4 blocks are not routable on the public internet by RFC. The most common are 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 (RFC 1918 private), 127.0.0.0/8 (loopback, RFC 5735), 169.254.0.0/16 (link-local, RFC 3927), 100.64.0.0/10 (carrier-grade NAT, RFC 6598), and 192.0.2.0/24 / 198.51.100.0/24 / 203.0.113.0/24 (documentation, RFC 5737). The tool tags any input that overlaps these.
How big can the IPv6 totals get?▼
IPv6 has 128 bits, so a /32 contains 2^96 addresses (around 79 octillion). The tool computes these as BigInt so the count is exact even for very small prefixes.
What is the practical limit on the subnet split?▼
The browser table caps at 4096 generated subnets to keep rendering fast. If you need more granular splits you typically want a script anyway.