Network and broadcast
The network address identifies the subnet. The broadcast address is the last address in normal IPv4 subnets.
IPv4 planning
Online IP Subnet Calculator
Use this IPv4 CIDR subnet calculator to find the network address, broadcast address, subnet mask, wildcard mask, host count, and usable IP range. A visual subnet table also shows consecutive network blocks.
Fast subnet mathGet network details without manual binary conversion.
Subnet summaryPreview consecutive networks for more-specific prefixes.
ACL helperWildcard mask output is ready for Cisco access lists.
IPv4 subnet calculator with CIDR and IP range
Enter an IPv4 address with optional CIDR, or choose a prefix from the list.
Subnetting reminders
Usable hosts
Most subnets reserve two addresses, but /31 and /32 networks are special cases used for point-to-point or host routes.
Wildcard masks
Wildcard masks are inverse subnet masks and are commonly used in Cisco ACLs and routing protocol network statements.
How to Use the Subnet Calculator
Enter an IPv4 address and prefix length when you need to confirm the network boundary before configuring a router, firewall, switch SVI, DHCP scope, VPN selector, or ACL. The calculator helps you avoid common subnetting mistakes such as using the network address as a host, placing a gateway outside the subnet, or writing a wildcard mask that matches more addresses than intended.
For design work, calculate the smallest prefix that gives enough usable host addresses while leaving room for growth. For troubleshooting, compare the calculated range with the device configuration. If two hosts cannot communicate, confirm that their IP addresses, masks, default gateways, and VLAN placement all agree with the subnet range shown here.
A common workflow is to calculate the subnet first, copy the network address into the routing or firewall plan, then use the first usable IP for the default gateway and reserve the final usable addresses for infrastructure such as firewalls, load balancers, or monitoring nodes. In WAN designs, verify whether the provider expects a /30, /31, or routed block before assigning addresses.
Common use cases
Plan VLAN gateways, DHCP pools, point-to-point links, firewall zones, static routes, and routing protocol network statements.
Configuration checks
Validate the subnet mask, first usable host, last usable host, broadcast address, and wildcard mask before pasting commands into a device.
Related practice
After calculating a subnet, test your understanding with the CCNA Fundamentals Test or the Routing Practice Test.
Related IP Tools
Use these related tools when the subnet calculation becomes part of a larger troubleshooting or documentation task.
Verify the Result Before Using It in a Configuration
The calculator should support a subnetting decision, not replace review. Confirm that the entered address belongs to the intended block, the prefix supplies enough usable addresses, and the proposed gateway and DHCP range do not use the network or broadcast address. For VLSM plans, compare each calculated range with the previous and next subnet to prevent overlap.
Document the result in CIDR notation and include the gateway, DHCP range, reserved addresses, VLAN, and purpose. A consistent record makes later firewall rules, route summaries, monitoring alerts, and troubleshooting much less ambiguous.
For example, 192.0.2.70/27 belongs to network 192.0.2.64. The block contains 32 addresses, the conventional usable range is 192.0.2.65 through 192.0.2.94, and the broadcast address is 192.0.2.95. The wildcard mask is 0.0.0.31. Those values can be used to review an SVI, DHCP scope, ACL or routing protocol statement.
Operational Uses for Subnet Results
- Size user, server, voice, wireless and management VLANs with room for expected growth.
- Define DHCP pools and exclusions that stay inside the correct subnet.
- Check whether two addresses are local to each other or require a default gateway.
- Create summary routes only when the component networks are contiguous and share the required prefix bits.
- Generate the inverse mask used by Cisco ACLs and some routing protocol network commands.
Special prefixes need separate interpretation. A /31 can be used on compatible point-to-point links without traditional network and broadcast addresses, while a /32 identifies one host route or loopback. Continue with the subnetting tutorial, wildcard mask calculator, and OSPF labs to apply the calculated networks.
IPv4 CIDR, IP range, and cloud subnet planning
Visual subnet calculator
The network summary displays consecutive IPv4 blocks in a table so you can compare network IDs, usable ranges, and broadcast addresses without doing binary conversion by hand.
IP range subnet calculator
Enter any host address with its CIDR prefix to identify the containing network, first and last conventional usable addresses, and broadcast address.
AWS subnet calculator guidance
Use the result to verify an IPv4 CIDR boundary and address range, but do not treat the displayed conventional host count as final cloud capacity. AWS reserves addresses within each subnet and applies platform-specific prefix rules, so confirm the current requirements before deployment.
IPv6 subnet calculator limitation
This page currently calculates IPv4 only. IPv6 uses 128-bit addresses, has no broadcast address, and requires IPv6-specific range and prefix calculations.
Subnet Calculator Frequently Asked Questions
What is a subnet calculator?
A subnet calculator converts an IP address and CIDR prefix or subnet mask into its network address, broadcast address, usable host range, address count, and related subnet details.
How do you use a subnet calculator?
Enter an IPv4 address, include or select a CIDR prefix, select Calculate, and review the network, mask, broadcast, first and last usable addresses, host count, and wildcard mask.
What is a subnet mask calculator?
A subnet mask calculator converts between a CIDR prefix and dotted-decimal mask, then uses that mask with an IP address to identify the network boundary and host range.
How do you find the subnet mask?
Enter the IP address with its CIDR prefix or select the prefix separately. The calculator converts the prefix into the corresponding dotted-decimal subnet mask.
How many hosts are in a subnet?
For conventional IPv4 subnets from /0 through /30, total addresses equal 2 raised to the number of host bits, and conventional usable hosts equal that total minus the network and broadcast addresses. Prefixes /31 and /32 require special interpretation.
How many subnets and hosts per subnet are available?
Borrowing n host bits creates 2n equal subnets. Each new subnet contains 2 raised to its remaining host bits, with two addresses conventionally excluded from host use except in special-prefix cases.
Which subnet does a host belong to?
Combine the host IP address with its CIDR prefix or subnet mask. The calculated network address identifies its subnet, and the entered address should fall within the displayed IP range.
What is my subnet mask?
A webpage cannot reliably detect the mask configured on your private device. Find the prefix in your device, router, DHCP, VPN, cloud, or administrator-provided settings, then enter it here to convert it to a subnet mask.
Does this subnet calculator support IPv6?
No. This version performs IPv4 subnet math only. Use an IPv6-specific calculator when working with 128-bit addresses and IPv6 prefix allocation.
How does this compare with other subnet calculators?
This is an independent online calculator for IPv4 CIDR, ranges, masks, and host counts. Users comparing Jodies subnet calculator, David's subnet calculator, Site24x7 subnet calculator, or other 24x7 subnet calculator results should verify that the same IP, prefix, and special-prefix rules are selected. Networking Essentials is not affiliated with those providers.