IP Subnet Calculator
Calculate IPv4 subnet details from CIDR notation
Invalid CIDR notation. Use the format 192.168.1.0/24 (octets 0-255, prefix 0-32).
Subnet Details
- Network Address
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- Broadcast Address
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- Subnet Mask
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- Wildcard Mask
- -
- First Usable Host
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- Last Usable Host
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- Usable Hosts
- -
- Total Addresses
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- IP Class
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- Mask (Binary)
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How to Use
- Enter a CIDR — Type an IPv4 address with a prefix length, such as
192.168.1.0/24, into the input field. - Calculate — Click Calculate or simply keep typing; results update automatically as you type.
- Copy the results — Use the Copy button to copy all subnet details to your clipboard.
Features
- Complete subnet details — Network address, broadcast address, subnet mask, wildcard mask, first and last usable host, and host counts in one view.
- /31 and /32 support — Point-to-point links (RFC 3021) and single-host routes are handled correctly.
- Binary mask view — See the subnet mask in binary to understand exactly how the prefix splits network and host bits.
- IP class detection — Automatically shows whether the address belongs to class A, B, C, D, or E.
- 100% client-side — All calculations run in your browser; no data ever leaves your device.
Use Cases
- Network planning: Split an address block into subnets for VLANs, offices, or cloud VPCs and verify the usable host range.
- Firewall and ACL configuration: Get the wildcard mask you need for Cisco ACL entries and OSPF statements.
- Certification study: Check your manual subnetting answers for CCNA, Network+, and other networking exams.
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Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation writes an IP address together with a prefix length, like 192.168.1.0/24. The number after the slash is how many leading bits of the 32-bit address identify the network; the remaining bits identify hosts inside that network.
Why does a /31 subnet have 2 usable hosts?
Traditionally the network and broadcast addresses are reserved, leaving zero usable hosts on a /31. RFC 3021 redefines /31 prefixes for point-to-point links, where broadcast is unnecessary, so both addresses are usable. This calculator follows RFC 3021 and reports 2 usable hosts for /31 and 1 for /32.
What is a wildcard mask used for?
A wildcard mask is the bitwise inverse of the subnet mask (for example, 0.0.0.255 is the inverse of 255.255.255.0). It is used in Cisco access control lists (ACLs) and OSPF network statements, where a 0 bit means "must match" and a 1 bit means "ignore".