IPv4 Subnet Calculator
Calculate CIDR boundaries, masks, host ranges, binary form, and equal-size IPv4 subnet splits.
Enter an IPv4 address with CIDR prefix such as 192.168.10.25/27, 10.0.0.0/24, or 172.16.5.128/26 to calculate network details.
Advanced Subnet Options
Split the input subnet into smaller subnets using a longer prefix.
Calculated Output
Subnet calculation output will appear here.
From one host address to the containing IPv4 prefix
IPv4 subnetting is used to divide address space into smaller, manageable network ranges. It appears in firewall rules, route tables, VPN configurations, cloud VPCs, security groups, access control lists, DHCP scopes, and infrastructure documentation.
This advanced IPv4 Subnet Calculator takes an address with CIDR prefix and calculates the network boundary, range end, directed-broadcast semantics, usable host range, subnet mask, wildcard mask, binary notation, and optional subnet splits. It is designed for practical DevOps, networking, and security troubleshooting tasks.
Reading the calculated boundary values
- Enter an IPv4 address with CIDR prefix, such as 192.168.10.25/27.
- Choose whether you want summary, table text, or JSON output.
- Enable binary notation when you want to inspect subnet math.
- Enable subnet splits to divide the range into smaller CIDR blocks.
- Click Calculate Subnet and copy the generated output.
Where subnet boundaries matter in configuration
- Calculating network and broadcast addresses from CIDR notation.
- Finding first and last usable host addresses.
- Converting prefix length into subnet mask and wildcard mask.
- Splitting a larger network into smaller subnets.
- Planning cloud VPC, firewall, VPN, or ACL network ranges.
- Documenting internal networks for operations and security teams.
Worked /27 boundary example
Input: 192.168.10.25/27 Calculated subnet: CIDR: 192.168.10.0/27 Network: 192.168.10.0 Broadcast: 192.168.10.31 Subnet mask: 255.255.255.224 Wildcard mask: 0.0.0.31 First usable: 192.168.10.1 Last usable: 192.168.10.30 Total addresses: 32 Usable hosts: 30
Prefix length controls address count and mask bits
CIDR prefix length tells you how many bits belong to the network portion of an IPv4 address. A /24 prefix means 24 network bits and 8 host bits. The equivalent subnet mask is 255.255.255.0.
Smaller prefix numbers create larger networks. Larger prefix numbers create smaller networks. For example, /24 contains 256 total addresses, while /27 contains 32 total addresses.
CIDR replaced classful network sizing
The Class A/B/C label is shown only as historical address context; the prefix length is what determines this calculation. RFC 4632 describes classless IPv4 routing, while RFC 3021 defines the special two-address /31 convention for point-to-point links.
IPv4 subnet edge cases
Why does a host address normalize to a network address?
An IPv4 subnet calculator takes an IP address and CIDR prefix and calculates network details such as subnet mask, network address, broadcast address, usable host range, and address counts.
How does the slash prefix change the range?
CIDR prefix length is the number after the slash, such as /24 or /27. It defines how many bits are used for the network portion of the IPv4 address.
Why are /31 and /32 different?
For prefixes /30 and shorter, this page shows the traditional network-and-directed-broadcast exclusion. A /31 is treated as two usable point-to-point endpoints under RFC 3021, so the second address is the range end rather than a directed broadcast on that link. A /32 represents one address and has no separate directed-broadcast address. Confirm platform-specific reservations and /31 support before turning a generic calculation into a cloud, firewall, DHCP, or LAN assignment.
Which subnet counts can divide a prefix evenly?
Yes. You can split a subnet by choosing a longer prefix or by entering an exact power-of-two subnet count. The preview is capped to keep the browser responsive.
Why is IPv6 not handled here?
This tool focuses on IPv4 subnet calculation. IPv6 subnetting has different address sizes and needs a separate interface.
Where does the IPv4 input go?
No. The calculation happens directly in your browser, and your IP addresses are not uploaded to a server.