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IP Subnet CIDR Calculator

Enter an IPv4 address and a CIDR prefix (like /24) to instantly see the subnet mask, network range and how many usable hosts fit inside it.

Subnet details

Enter an IPv4 address and CIDR prefix.

Usable hosts—Enter an IP and CIDR prefix above.
Subnet mask—
Network address—
Broadcast address—
Usable host range—
Quick insight

IP Subnet CIDR Calculator

Enter an IP address and CIDR prefix to see the full subnet breakdown.

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What Is an IP Subnet CIDR Calculator?

CIDR (Classless Inter-Domain Routing) notation writes a subnet as an IP address plus a slash and a number, like 192.168.1.0/24. That number is the prefix length — how many bits of the 32-bit IPv4 address are fixed as the network portion. This calculator takes any address and prefix and works out the full subnet: mask, network address, broadcast address, and the usable range of host addresses.

This is the exact bitwise math routers and switches use internally, made visible so you can plan networks, assign static IPs, or troubleshoot connectivity without doing binary math by hand.

How to Read Your Results

Subnet Mask

The dotted-decimal equivalent of your CIDR prefix — for example /24 is 255.255.255.0. It marks which bits of an address are "network" versus "host."

Network Address & Broadcast Address

The network address identifies the subnet itself and the broadcast address is reserved for sending to every host on it — neither is assignable to a device on subnets /30 or larger.

Usable Host Range & Usable Hosts

The range of addresses you can actually assign to devices, and the total count. This excludes the network and broadcast addresses except in the special /31 (2 usable, point-to-point) and /32 (1 usable, single host) cases.

Real-World Example

You're setting up a small office LAN and give it 192.168.1.10/24.

FieldValue
Subnet mask255.255.255.0
Network address192.168.1.0
Broadcast address192.168.1.255
Usable hosts254 (192.168.1.1 – 192.168.1.254)

A /24 always gives you 254 usable addresses regardless of which /24 network you're on — only the first three octets change between networks.

Tips for Subnetting

  • Smaller prefix number = bigger network. A /16 has far more addresses than a /28.
  • Reserve room to grow — pick a prefix with more usable hosts than you currently need.
  • Point-to-point links commonly use /30 or /31 to minimize wasted address space between two routers.
  • Private address ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are reserved for internal networks and won't route on the public internet.

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Note: This calculator covers standard IPv4 CIDR subnetting only. It does not account for IPv6, VLSM route summarization across multiple subnets, or provider-specific reserved address policies.

Last updated: August 2026 · Reviewed by: Simple Calculator Tools Editorial Team