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Subnet Calculator

IPv4 network broadcast host ranges from CIDR.

About Subnet Calculator

Subnet Calculator on UtilityKit resolves any IPv4 CIDR block into its full set of network parameters instantly in your browser. Enter a network like 192.168.1.0/24 and receive the network address, broadcast address, subnet mask in dotted-decimal, wildcard mask, usable host IP range, and total host count — all computed with no server required. The tool validates input and corrects host-bit errors silently, converting 192.168.1.50/24 to the canonical 192.168.1.0/24. Paste multiple CIDR blocks to check for overlaps and summarise address space allocation — useful when designing VPCs, reviewing firewall rules, or documenting a network topology. Whether you are a network engineer planning a data-centre migration, a developer configuring cloud security groups, or a student preparing for the CCNA exam, the calculator eliminates manual binary arithmetic and the common off-by-one errors that.

Why use Subnet Calculator

Eliminates Binary Arithmetic

Converting CIDR to subnet mask and host ranges by hand requires error-prone binary AND operations. The calculator handles all bit arithmetic instantly and accurately.

Cloud & Firewall Ready

AWS VPC, Azure VNET, GCP VPC, and most firewall UIs accept CIDR input directly. Verify your address ranges before entering them to avoid over-permissive or broken rules.

Overlap Detection

Paste multiple CIDR blocks to check whether subnets overlap — catches double-allocation mistakes before they cause routing conflicts in production.

VLSM Planning

Adjust prefix lengths interactively to size subnets for different departments or availability zones without maintaining a spreadsheet.

Exam & Study Aid

CCNA, CompTIA Network+, and similar certifications test subnet calculations. This tool lets you check your manual work instantly during practice.

Fully Browser-Side

Internal IP addresses and network topologies never leave your device — all computation runs locally with no server round-trip.

How to use Subnet Calculator

  1. Enter an IPv4 address in CIDR notation into the input field — for example 10.0.0.0/8 or 192.168.100.64/26.
  2. If you enter a host address instead of the network address (e.g. 192.168.1.50/24), the tool automatically corrects it to the canonical network address 192.168.1.0/24.
  3. Read the results panel: network address, broadcast address, subnet mask (dotted-decimal), wildcard mask, first usable host, last usable host, and total usable host count.
  4. Note the total host count formula: 2^(32−prefix) − 2, subtracting the network and broadcast addresses. A /30 gives 2 hosts; a /24 gives 254.
  5. For VLSM planning, adjust the prefix length and observe how host count and address range change — incrementing from /24 to /25 halves the usable hosts.
  6. Copy any individual field value with the copy icon, or copy the full summary block to paste into documentation or a network diagram tool.

When to use Subnet Calculator

  • When designing a VPC or VNET and you need to confirm that your planned CIDR blocks do not overlap and provide enough host addresses for each tier.
  • When writing firewall or security group rules and you need the exact network address and mask to avoid accidentally allowing too broad a range.
  • When troubleshooting a routing issue and you need to verify whether a given IP falls within a particular subnet's host range.
  • When documenting a network topology and you need broadcast addresses, wildcard masks, or host counts for every segment.
  • When studying for CCNA, Network+, or similar networking certifications and you want to verify your manual subnet calculations.
  • When migrating an on-premise network to a cloud provider and you need to translate legacy subnet masks (e.g. 255.255.255.0) into CIDR prefix lengths.

Examples

Standard /24 LAN subnet

Input: 192.168.1.0/24

Output: Network: 192.168.1.0 | Broadcast: 192.168.1.255 | Mask: 255.255.255.0 | Wildcard: 0.0.0.255 | Hosts: 192.168.1.1–192.168.1.254 (254 usable)

Small /30 point-to-point link

Input: 10.0.0.0/30

Output: Network: 10.0.0.0 | Broadcast: 10.0.0.3 | Mask: 255.255.255.252 | Wildcard: 0.0.0.3 | Hosts: 10.0.0.1–10.0.0.2 (2 usable)

AWS VPC /16 supernet

Input: 172.31.0.0/16

Output: Network: 172.31.0.0 | Broadcast: 172.31.255.255 | Mask: 255.255.0.0 | Hosts: 172.31.0.1–172.31.255.254 (65,534 usable)

Tips

  • For point-to-point WAN links between two routers, use a /30 (2 usable hosts) to conserve address space instead of wasting a /24 on a two-device link.
  • When planning a three-tier VPC (web, app, database), allocate larger subnets (/23 or /22) to tiers that auto-scale and smaller ones (/27 or /28) to tightly controlled database tiers.
  • The subnet mask in dotted-decimal maps directly to CIDR: 255.255.255.0 = /24, 255.255.255.128 = /25, 255.255.255.192 = /26, 255.255.255.224 = /27.
  • Always leave at least one /16 block unallocated when designing a large-organisation address plan — growth inevitably requires more space than initially estimated.
  • Cross-check your output against RFC 1918 private ranges: if your subnet contains 10.x.x.x, 172.16-31.x.x, or 192.168.x.x addresses, it is non-routable on the public internet and appropriate for internal use only.

Frequently Asked Questions

What is CIDR notation?▾
Classless Inter-Domain Routing (CIDR) notation expresses an IP address and its network prefix length together, separated by a slash — for example 192.168.1.0/24. The number after the slash indicates how many bits are used for the network portion, with the remaining bits available for host addresses.
Why are two host addresses subtracted from the total?▾
The first address in any subnet (all host bits zero) is reserved as the network address, and the last address (all host bits one) is the broadcast address. Both are unusable by individual hosts. A /24 has 256 total addresses but only 254 usable hosts.
What is a wildcard mask?▾
A wildcard mask is the bitwise inverse of the subnet mask. Where the subnet mask has 1s (network bits), the wildcard has 0s, and vice versa. Wildcard masks are used in Cisco ACLs and OSPF configuration to specify which bits of an address must match.
What prefix length gives exactly 30 usable hosts?▾
A /27 prefix gives 32 total addresses minus 2 = 30 usable hosts. A /26 gives 62, a /28 gives 14. Use the calculator to explore the relationship between prefix length and host count interactively.
Can this calculator handle /31 and /32 prefixes?▾
Yes. A /31 subnet (RFC 3021) has 2 addresses with no reserved network or broadcast — both are usable for point-to-point links. A /32 is a host route representing exactly one IP address. Both are displayed correctly.
Does the tool support IPv6 subnetting?▾
This tool is focused on IPv4 CIDR subnetting. For IPv6 address representation and conversion, see the IPv4 to IPv6 Converter tool on UtilityKit.
What is VLSM and how does this tool help?▾
Variable Length Subnet Masking (VLSM) allows different subnets within the same address space to have different prefix lengths, optimising IP allocation. This tool lets you calculate parameters for each individual CIDR block so you can confirm sizes and detect gaps or overlaps when building a VLSM scheme.
What is the largest private IP range I can subnet?▾
The three RFC 1918 private ranges are 10.0.0.0/8 (16,777,214 hosts), 172.16.0.0/12 (1,048,574 hosts), and 192.168.0.0/16 (65,534 hosts). Enter any of these CIDR blocks to see the full address range before dividing it into smaller subnets.

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Glossary

CIDR
Classless Inter-Domain Routing — a method for allocating IP addresses using a variable-length prefix instead of the fixed class system (Class A/B/C). Written as address/prefix-length, e.g. 10.0.0.0/8.
Network Address
The first address in a subnet, where all host bits are zero. Identifies the subnet itself and cannot be assigned to any host device.
Broadcast Address
The last address in a subnet, where all host bits are one. Packets sent to this address are delivered to all hosts in the subnet. It cannot be assigned to a host.
Subnet Mask
A 32-bit number that divides an IP address into network and host portions. Written in dotted-decimal (e.g. 255.255.255.0) or as a prefix length after a slash (e.g. /24).
Wildcard Mask
The bitwise inverse of the subnet mask. Used in Cisco ACL and OSPF configurations to specify which bits of an address are significant. A /24 subnet mask of 255.255.255.0 has wildcard mask 0.0.0.255.
VLSM
Variable Length Subnet Masking — the practice of subdividing an address space into subnets of different sizes by using different prefix lengths, allowing efficient allocation of IP addresses across networks with varying host counts.