IPv4 CIDR & Subnet Mask Calculator

What is cidr / subnet calculator?

CIDR notation (`192.168.1.0/24`) packs an IP address and a subnet size into one compact string, but reading the actual boundaries of that subnet — where it starts, where it ends, and how many real hosts fit inside it — means doing binary arithmetic in your head. This tool does that arithmetic for you: enter an address in CIDR notation, or an address with a dotted subnet mask, and it calculates the network address, broadcast address, usable host range, netmask, wildcard mask and total/usable address counts, along with a binary breakdown showing exactly which bits are the network portion and which are host bits.

When to use it

• Working out the usable host range for a subnet before assigning static IPs on it.
• Checking whether two subnets overlap or a given address actually falls inside a documented CIDR block.
• Converting between a prefix length (/24) and a dotted subnet mask (255.255.255.0) in either direction.
• Understanding firewall or routing rules written in CIDR notation, including which addresses in a range are private, loopback or multicast.

How to use this tool

1. Enter an address in CIDR notation ("192.168.1.0/24"), or an address and mask separated by a space ("192.168.1.0 255.255.255.0").
2. Read the network address, broadcast address and usable host range for that subnet.
3. Check the binary breakdown to see exactly which bits are fixed (network) and which vary (host) — the boundary lines up with the prefix length.
4. Copy a link that restores this exact address to share with a teammate.

Example

A standard 256-address home/office subnet.

Input

192.168.1.0/24

Output

Network      192.168.1.0/24
Broadcast    192.168.1.255
Host range   192.168.1.1 – 192.168.1.254
Netmask      255.255.255.0
Usable hosts 254

Entering any address inside the block, like 192.168.1.130/24, produces the same network and broadcast — the calculator always resolves to the block's actual boundaries.