What Subnet Calculator helps you do

Enter an IPv4 address and CIDR prefix to calculate network address, broadcast, subnet mask, wildcard mask, host range, and usable host count. Built for planning and troubleshooting — not for live network configuration without verifying against your design standard. It is the quick arithmetic check before a VLAN plan, a firewall rule or a routing change.

Addresses you type are processed locally in your browser and are not sent to Haivix servers.

How it works

Haivix parses dotted-decimal IPv4, validates octets, applies the CIDR mask, and derives network/broadcast boundaries. /31 and /32 follow common IPv4 conventions shown in the results panel. The arithmetic is performed locally; no request is sent to the address or to a network service.

How to use Subnet Calculator

Enter an address in CIDR form such as 192.168.10.10/24.
Confirm the prefix field if the input omits it.
Read network, mask, first and last host, total addresses, and usable hosts.
Copy the values into your IP plan and check the gateway and reserved addresses separately.

When to use it

Planning lab or office subnet splits before deployment
Explaining CIDR boundaries during troubleshooting or study
Checking whether an address falls in a private RFC 1918 range
Confirming the host range before writing a firewall rule
Documenting a VLAN plan in a ticket or runbook
Checking a /31 point-to-point link or a /32 host route

When not to use it

IPv6 planning (use an IPv6-specific tool)
Authoritative IPAM or DHCP configuration without change control
Determining effective policy routes or ACL hit counts in production
Discovering which addresses are live on the network

Example

192.168.1.10/24 yields network 192.168.1.0, broadcast 192.168.1.255, usable hosts 192.168.1.1–192.168.1.254 (254 usable addresses). A /31 point-to-point link has two addresses and no broadcast under the common convention, while a /32 describes a single host route.

What you can do with Subnet Calculator

Parse an IPv4 address with a CIDR prefix such as /24.
Show the network address and broadcast address.
Show the dotted subnet mask and wildcard mask.
List the first and last usable host addresses.
Report total addresses and usable host count.
Label private and public ranges as a quick heuristic.

Example: split an office network

Start with the current range and prefix, then calculate the boundaries before assigning anything. Writing the network and broadcast addresses into the plan prevents the classic mistake of giving a host the address reserved for the subnet itself.

If the range must be split, calculate each proposed prefix on its own and check the first and last host of every piece. Overlapping ranges are easier to spot in a table than in a spreadsheet formula.

Copy the network, mask and host range into the ticket, then confirm the gateway and reserved addresses against the actual DHCP or IPAM configuration. The calculator does not know which addresses are already in use.

What to know before you start

IPv4 only; no VLSM planner across multiple subnets in one view.
Private/public scope is a heuristic label, not a routing policy decision.
Calculations happen locally but do not ping or validate live address usage.
It does not calculate wildcard masks for every vendor syntax or check ACL semantics.
It does not account for reserved addresses inside a DHCP pool.

Common mistakes

Forgetting that network and broadcast addresses are not usable on typical LAN subnets
Mixing up wildcard mask with subnet mask when writing ACLs
Applying /31 semantics from one vendor document without checking your platform
Assuming a private range is automatically safe without a firewall policy
Assigning a gateway address that falls outside the calculated host range
Planning overlapping subnets and discovering the overlap after deployment

Troubleshooting

If the calculator rejects the input, check that each octet is between 0 and 255 and that the prefix is between 0 and 32.

If the host count looks off by two, remember that a typical subnet reserves the network and broadcast addresses. /31 and /32 are special cases.

If the result does not match your IPAM, confirm that the IPAM is showing the same prefix and not a summarized supernet.

If a device cannot reach a host in the calculated range, the address may be outside the device's configured mask or the route may point elsewhere. The calculator only describes the subnet, not the live routing table.

If the range is private but traffic still leaves the network, check the firewall and NAT rules; the label is not a security control.

Subnet Calculator