IP Subnet Calculator – CIDR, Network & Host Calculator

An IP subnet calculator is a network calculator that computes network address, broadcast address, usable host range, subnet mask, wildcard mask, and CIDR prefix from an IPv4 or IPv6 address.

Subnetting splits one IP network into smaller subnetworks so administrators can reduce broadcast domains, improve security, and allocate addresses efficiently.

A subnet mask (or CIDR prefix) tells devices which bits identify the network and which bits identify hosts. This free ip subnet calculator applies the same math used in RFC-based networking and Cisco-style ACL planning.

Follow these steps to calculate subnet details:

• Step 1: Open the IPv4 or IPv6 tab.
• Step 2: Enter an IPv4 address (for example 192.168.1.10).
• Step 3: Choose a CIDR prefix from the subnet dropdown or type a subnet mask (255.255.255.0 or /24).
• Step 4: Optionally filter prefixes by legacy network class (A, B, C, or Any).
• Step 5: Click Calculate and review network, broadcast, host range, masks, and host counts.
• Step 6: Copy results for documentation, ACLs, or cloud VPC design.

• Network segmentation — divide one large prefix into VLANs, departments, or availability zones.
• Broadcast domain reduction — smaller subnets limit broadcast traffic.
• Improved security — ACLs and firewalls can reference precise CIDR blocks.
• Better IP management — allocate only the addresses each segment needs.
• Efficient routing — summarize routes with aggregate prefixes.

CIDR replaces class-based networking with flexible prefix lengths. Common examples:

• /8 — very large networks (class A legacy)
• /16 — regional or campus networks (class B legacy)
• /24 — typical LAN (254 usable IPv4 hosts)
• /25 — 126 usable hosts
• /26 — 62 usable hosts
• /27 — 30 usable hosts
• /28 — 14 usable hosts
• /29 — 6 usable hosts
• /30 — point-to-point links (2 usable hosts)

CIDR prefix, dotted-decimal mask, and typical usable host counts:

• Network Address — first address in the subnet (host bits all 0).
• Broadcast Address — last address (host bits all 1).
• First / Last Usable Host — assignable addresses between network and broadcast.
• Total Hosts — all addresses in the subnet including reserved ones.
• Usable Hosts — assignable count (usually total minus 2).
• Subnet Mask — dotted-decimal network mask.
• CIDR Prefix — slash notation (e.g. /24).
• Wildcard Mask — inverse mask for Cisco ACLs.

IP 192.168.1.10 with prefix /24:

• Better performance — smaller broadcast domains and summarized routing.
• Improved security — micro-segmentation and least-privilege ACLs.
• Reduced broadcast traffic — limits ARP and discovery storms.
• Efficient address allocation — right-size subnets for each workload.
• Simplified management — document CIDR blocks per site or VPC.

• Enterprise networks — office LANs, Wi‑Fi, and server VLANs.
• Data centers — rack and pod addressing.
• Cloud infrastructure — AWS, Azure, and GCP VPC subnets.
• ISP networks — customer allocations and aggregation.
• Home labs — practice with 192.168.x.x /24 splits.
• Cybersecurity — scope penetration tests and firewall rules.
• Virtual Private Clouds (VPC) — public/private subnet design.

Both describe the same boundary; notation differs by context:

• IPv4 — 32-bit addresses written as four octets.
• CIDR — classless prefix lengths such as /24.
• Gateway — router IP on a subnet (often first usable host).
• DNS — name resolution; unrelated to mask math but used with IP planning.
• Broadcast Address — reaches all hosts on the L2 segment.
• Private IP — RFC 1918 space not routed on the internet.
• Public IP — globally routable addresses.
• Network Address — identifies the subnet.
• Host Address — assignable device address.

Continue network planning on this site:

• IP Lookup
• IP Geolocation
• IPv6 Test
• Hostname Lookup
• Reverse DNS Lookup
• DNS Lookup
• WHOIS Lookup
• Ping Test

• RFC 4632 — Classless Inter-domain Routing (CIDR)
• RFC 950 — Internet Standard Subnetting Procedure
• IANA IPv4 Address Space Registry
• Cisco — IP Addressing and Subnetting

This subnet calculator is intended for educational, administrative, and network planning purposes. Always verify production network configurations, routing tables, and cloud provider limits before deployment.