IPv4 Subnet Calculator
Enter an IPv4 address with a CIDR prefix or subnet mask to get the network address, broadcast address, usable host range, host count, subnet and wildcard masks, binary view and address type. Add a number to split the network into equal subnets. It handles /31 point-to-point links and /32 host routes correctly, and is handy for CCNA practice and real network planning.
IPv4 Subnet Calculator
Binary
Runs in your browser. Nothing you enter is uploaded or saved.
How to use this tool
- Enter the address. Type an IPv4 address, or CIDR notation such as 10.0.0.0/22.
- Enter the prefix or mask. Use a prefix like /26 or a mask like 255.255.255.192.
- Calculate. Press Calculate to see the addresses, host range, masks and binary.
- Split if needed. Enter how many subnets you need to see the resulting networks and ranges.
How usable hosts are counted
A subnet with prefix /n has 232−n addresses. Normally the first (network) and last (broadcast) are reserved, leaving 232−n − 2 usable hosts: a /24 has 254, a /26 has 62.
/31 and /32 are special
RFC 3021 allows /31 on point-to-point links, where both addresses are usable and there is no broadcast. A /32 identifies a single host, used for loopbacks and host routes.
Private and special ranges
RFC 1918 private ranges are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Other special ranges include loopback 127.0.0.0/8, link-local 169.254.0.0/16 and shared address space for carrier-grade NAT, 100.64.0.0/10.
Wildcard masks
A wildcard mask is the inverse of the subnet mask (for /26, 0.0.0.63). Cisco ACLs and OSPF network statements use it to say which bits can vary.
Frequently asked questions
What is CIDR notation?
Classless Inter-Domain Routing writes the mask as the number of network bits after a slash, so 255.255.255.0 becomes /24.
Are address classes still used?
Not for routing; classless addressing replaced them in 1993. The class is shown because it still appears in exams and older material.
Does it support IPv6?
Not yet. This calculator is for IPv4 only.