IP Subnet Calculator — CIDR & Subnet Mask

IPv4 address with CIDR

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How to use IP Subnet Calculator

Enter an IP address and a CIDR prefix (/24) or subnet mask.
Read the breakdown — network, broadcast, usable host range, host count, mask.
Plan or configure — allocate segments, set router/firewall/VLAN values.
Remember network + broadcast aren't usable — that's the "minus 2" for host counts.

What is IP Subnet Calculator?

An IP subnet calculator takes an IP address and subnet mask (or CIDR notation like /24) and computes the network's properties: the network address, broadcast address, the range of usable host addresses, and how many hosts the subnet holds. It's the essential arithmetic of IP networking, done instantly instead of by error-prone binary math.

Subnetting divides IP address space into networks — deciding how many addresses each network segment gets and where its boundaries fall. The math is binary (masks operate bit-by-bit on addresses), which makes hand-calculation slow and mistake-prone; a calculator turns "what's the usable range of 192.168.1.0/26?" into an instant answer.

About the IP Subnet Calculator

Enter an IP address and a CIDR prefix or subnet mask, and get the full subnet breakdown.

What it computes and why it matters: network address (the subnet's identifier — first address, not usable for a host); broadcast address (the last address, reserved for broadcasting — also not a usable host); usable host range (the addresses you can actually assign to devices — network+1 through broadcast-1); total/usable hosts (a /24 has 256 addresses, 254 usable; a /26 has 64, 62 usable — the subtract-2 for network and broadcast); and the mask in both CIDR (/24) and dotted-decimal (255.255.255.0) forms.

Who uses it: network administrators planning IP allocation (how to divide a network into segments of the right sizes), configuring routers, firewalls and VLANs (which need exact network/mask values), studying for networking certifications (subnetting is a core, heavily-tested skill), and anyone setting up home/office networks or cloud VPCs (which are defined by CIDR blocks). The CIDR shorthand: the number after the slash is how many bits are the network portion — higher = smaller subnet (/30 is 4 addresses, /16 is 65,536). Everything computes locally and instantly.

Frequently Asked Questions

CIDR notation — the number of bits that are the network portion. /24 means the first 24 bits (three octets) identify the network, leaving 8 bits (256 addresses) for hosts. Higher numbers = smaller subnets; /30 is 4 addresses, /16 is 65,536.

Two addresses are reserved: the network address (first, identifies the subnet) and the broadcast address (last, for broadcasting to all hosts). Neither can be assigned to a device, so a 256-address /24 has 254 usable — the universal "minus 2".

Two notations for the same thing: /24 (CIDR) equals 255.255.255.0 (dotted-decimal mask). CIDR is compact and modern; dotted masks appear in older configs and some interfaces. The calculator shows both.

Increase the CIDR prefix — a /24 splits into two /25s (128 addresses each), four /26s (64 each), etc. Each higher bit halves the subnet size. The calculator shows each subnet's exact range so you can plan the division.

Network address = the first address, identifying the subnet itself (192.168.1.0 for a /24). Broadcast address = the last (192.168.1.255), used to send to all hosts at once. Both are reserved; usable hosts are everything between them.