IPv4 CIDR math — netmask, network, broadcast, host range and binary view.
Updated
Quick start
Enter a CIDR like 192.168.1.0/24, get netmask, network, broadcast, host range and binary view.
Type an IPv4 address with an optional /n prefix. Examples: 10.0.0.0/8, 192.168.1.0/24, 172.16.4.32/27.
Use the /8 to /32 preset buttons to try different prefixes instantly. The math updates as you type.
Netmask, network and broadcast addresses, usable host range, RFC-1918 / loopback / link-local flags and a binary breakdown of address and mask.
In-depth guide
Enter a CIDR address like 192.168.1.0/24 and see the netmask, wildcard mask, network address, broadcast, usable host range and binary breakdown. Every computation runs locally.
A CIDR block x.x.x.x/n describes a contiguous range of IPv4 addresses by saying "the first n bits are the network, the remaining 32-n bits are hosts".
So 192.168.1.0/24 is the 256-address range from 192.168.1.0 to 192.168.1.255, with the first three octets (24 bits) fixed and the last octet (8 bits) free for hosts.
The number of addresses in a /n block is 2^(32-n). A /24 has 256, a /16 has 65,536, a /30 has 4.
In a normal subnet two addresses are reserved:
This is why a /24 has 256 total addresses but only 254 usable hosts.
Two exceptions exist:
Not every IPv4 address can be used on the public internet. The tool flags well-known reserved ranges in the output:
10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. Intended for internal networks behind NAT.127.0.0.0/8. Packets never leave the device.169.254.0.0/16. Self-assigned by the OS when DHCP is unavailable; only valid on the same Ethernet segment.CIDR (Classless Inter-Domain Routing) writes an IPv4 address and its network prefix as 'x.x.x.x/n', where n is the number of leading bits that belong to the network. For example, 192.168.1.0/24 means the first 24 bits identify the network and the last 8 bits identify hosts within it.
In a normal subnet, two addresses are reserved: the network address (all host bits 0) and the broadcast address (all host bits 1). So a /24 has 256 total addresses but only 254 usable for hosts. Exceptions: /31 reserves none (point-to-point links per RFC 3021), /32 represents a single host (no reservation).
The 32-bit IPv4 address is shown grouped by octet (each octet being 8 bits, separated by dots). Compare the address against the netmask line — every bit where the mask is '1' is fixed (the network), every bit where the mask is '0' is the host portion.
10.0.0.0/8 (16,777,216 addresses), 172.16.0.0/12 (1,048,576 addresses) and 192.168.0.0/16 (65,536 addresses). These are reserved for private internal networks and are not routable on the public internet.
127.0.0.0/8 is the loopback range — packets are delivered locally and never leave the device. 169.254.0.0/16 is link-local (RFC 3927) — automatically assigned by the OS when DHCP fails, and only valid on the same Ethernet segment.
Classful networking is mostly obsolete (replaced by CIDR in 1993), but the labels persist. Class A is 0.0.0.0–127.255.255.255 (default mask /8). Class B is 128–191 (/16). Class C is 192–223 (/24). Class D is 224–239 (multicast). Class E is 240–255 (reserved / experimental).
Not yet. IPv6 addresses are 128 bits and need BigInt math for clean handling. We may add a separate IPv6 tool — for now this tool is strictly IPv4 / CIDR /0 through /32.
No. All the bit math runs in your browser. The CIDR you enter never leaves your device.
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