CIDR Visualizer & Subnet Calculator

Networking

Visualize any IPv4 CIDR block. See the binary breakdown with the network/host boundary highlighted, the address range as a bar, and split a network into smaller subnets or aggregate adjacent ones into one supernet.

Network
192.168.1.0/24
Total addresses
256
Usable hosts
254
IP type
Public

Address Range

N
254 usable hosts
B
Network
192.168.1.0
First usable
192.168.1.1
Last usable
192.168.1.254
Broadcast
192.168.1.255

Binary Breakdown

Network bits in red, host bits in green. The vertical line is the /24 mask boundary.

IP address
11000000.10101000.00000001.00000000
Subnet mask
11111111.11111111.11111111.00000000
Network address
11000000.10101000.00000001.00000000
Broadcast address
11000000.10101000.00000001.11111111

Network Details

Subnet mask255.255.255.0
Wildcard mask0.0.0.255
CIDR/24
IP classC
Hex0xC0A80100

Reverse Lookups

Reverse DNS (PTR)
168.1.192.in-addr.arpa
Range
192.168.1.0 – 192.168.1.255

Split into smaller subnets

→ 4 subnets
CIDRNetworkFirst usableLast usableBroadcastHosts
192.168.1.0/26192.168.1.0192.168.1.1192.168.1.62192.168.1.6362
192.168.1.64/26192.168.1.64192.168.1.65192.168.1.126192.168.1.12762
192.168.1.128/26192.168.1.128192.168.1.129192.168.1.190192.168.1.19162
192.168.1.192/26192.168.1.192192.168.1.193192.168.1.254192.168.1.25562

Supernet (CIDR aggregation)

Paste two or more CIDR blocks (one per line) and we'll find the smallest single CIDR that contains all of them — the inverse of subnetting.

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation writes an IPv4 network as address/prefix, where the prefix is the number of leading 1-bits in the subnet mask. For example, 192.168.1.0/24 means a 24-bit network mask (255.255.255.0), giving 256 total addresses with 254 usable hosts.

CIDR was introduced in RFC 1519 (1993) to replace the wasteful Class A/B/C system. With CIDR, network sizes are no longer fixed at 8, 16, or 24 bits — you can allocate exactly as much address space as needed.

How to read the binary visualization above

The mask boundary at /24 splits each address into two parts:

  • The network bits (left of the boundary) are identical for every address in the subnet. Setting them all and zeroing the rest gives the network address.
  • The host bits (right of the boundary) vary across the addresses in the subnet. All zeros = network address, all ones = broadcast address, everything in between is a usable host.
  • The subnet mask is just N ones followed by (32 − N) zeros — there is no other valid form. 255.255.255.192 is /26 because 11111111.11111111.11111111.11000000 has 26 leading 1s.

How many usable hosts in each subnet size?

CIDRSubnet maskTotalUsable hostsTypical use
/8255.0.0.016,777,21616,777,214Large enterprise / former Class A
/16255.255.0.065,53665,534Campus network / former Class B
/22255.255.252.01,0241,022Mid-size office
/24255.255.255.0256254Small office / VLAN
/25255.255.255.128128126Half a /24
/26255.255.255.1926462Quarter of a /24
/27255.255.255.2243230AWS subnet minimum
/28255.255.255.2401614Small DMZ
/29255.255.255.24886Server cluster
/30255.255.255.25242Point-to-point WAN link
/31255.255.255.25422RFC 3021 P2P (no broadcast)
/32255.255.255.25511Single host route

Usable hosts = 2(32 − prefix) − 2 for IPv4 subnets smaller than /31 (the network and broadcast addresses are reserved). /31 and /32 are special cases.

Reserved IPv4 ranges to remember

  • 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 — RFC 1918 private ranges, not routable on the public internet.
  • 127.0.0.0/8 — loopback, for software talking to itself on a host.
  • 169.254.0.0/16 — link-local (APIPA), used when DHCP fails.
  • 100.64.0.0/10 — RFC 6598 carrier-grade NAT.
  • 224.0.0.0/4 — multicast (everything starting with 224 to 239).
  • 0.0.0.0/8 and 240.0.0.0/4 — reserved or special-use.

Frequently Asked Questions

What is the difference between subnet mask and CIDR notation?

They describe the same thing in different forms. 192.168.1.0 255.255.255.0 and 192.168.1.0/24 are equivalent — the /24 is just a count of leading 1-bits in the mask. CIDR notation is shorter and is the modern standard.

How many usable hosts are in a /24 subnet?

A /24 has 256 total addresses and 254 usable hosts. Two addresses are always reserved: the network address (.0, all host bits 0) and the broadcast address (.255, all host bits 1).

Why is /31 special?

RFC 3021 allows /31 subnets on point-to-point links to use both addresses, with no network or broadcast address. Without this, every WAN link between two routers would waste 2 of 4 addresses. /31 is now standard practice on router-to-router links.

What is supernetting (CIDR aggregation)?

Combining several adjacent smaller CIDR blocks into one larger block. For example, 192.168.0.0/24 + 192.168.1.0/24 aggregates into 192.168.0.0/23. The blocks must be contiguous, the same size, and aligned on a power-of-two boundary.

How is the broadcast address calculated?

Take the network address and set all host bits to 1. For 192.168.1.0/24, the host bits are the last 8, so the broadcast is 192.168.1.255. For 10.5.0.0/14, the host bits are the last 18, so the broadcast is 10.7.255.255.

What is the wildcard mask?

The bitwise inverse of the subnet mask. For /24, the mask is 255.255.255.0 and the wildcard is 0.0.0.255. Cisco ACLs and OSPF use wildcard masks because matching on host bits is the natural operation for those protocols.

Need only the basic numbers? See the simpler IP/Subnet Calculator. For binary/hex conversion outside networking, the Number Base Converter handles arbitrary bases.