Networking · IPv4 · CIDR
IP Subnet
Calculator
Enter any IPv4 address with a CIDR prefix to instantly get network address, broadcast, usable hosts, subnet mask, and binary breakdown. Includes subnet splitter and CIDR reference.
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Network
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Usable Hosts
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Class
IPv4 CIDR Calculator
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Common Networks
Split Network into Subnets
Enter a base network and choose how many equal subnets to create.
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CIDR Quick Reference
Click any row to load it into the IPv4 calculator.
subnet_calc v2.0
IP_ADDR—
NETWORK—
BROADCAST—
FIRST_HOST—
LAST_HOST—
SUBNET_MASK—
USABLE_HOSTS—
IP_CLASS—
Total IPs
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Usable Hosts
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Network Bits
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Host Bits
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Subnet Details
🔢 Binary Representation
📋 Complete CIDR / Subnet Mask Reference
IP Subnetting Explained
IP subnetting divides a network into smaller subnetworks (subnets) for better organization, security, and IP address management. The CIDR notation combines an IP address with a prefix length (e.g., 192.168.1.0/24) to define the network.
Key Subnet Formulas
Subnet Mask: CIDR /n → first n bits = 1, rest = 0
Network Addr: IP AND subnet_mask
Broadcast: IP OR (NOT subnet_mask)
Usable Hosts: 2^(32-n) - 2 (subtract network + broadcast)
Total IPs: 2^(32-n)
First Host: network_address + 1
Last Host: broadcast_address - 1
Private ranges: 10.0.0.0/8 (16M hosts)
172.16.0.0/12 (1M hosts)
192.168.0.0/16 (65K hosts)
Loopback: 127.0.0.0/8
Link-local: 169.254.0.0/16
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation writes an IP address followed by a slash and a number indicating how many bits are used for the network portion. For example, 192.168.1.0/24 means the first 24 bits (192.168.1) identify the network, and the last 8 bits (0–255) identify individual hosts. This replaced the older Class A/B/C system and allows more flexible, efficient IP allocation. The /24 network has 256 total IPs, 254 usable (subtracting network address and broadcast).
Why are 2 IP addresses reserved in each subnet?
Every subnet reserves 2 addresses: the network address (all host bits = 0, used to identify the subnet itself) and the broadcast address (all host bits = 1, used to send a packet to every host in the subnet). So a /24 subnet has 256 total IPs but only 254 usable host addresses. A /30 subnet (used for point-to-point links) has 4 IPs total, 2 usable — one for each end of the link. A /32 represents a single host (no host bits).
What are the private IP address ranges?
RFC 1918 defines three private IP ranges not routed on the public internet: Class A — 10.0.0.0/8 (10.0.0.0–10.255.255.255, ~16.7 million addresses). Class B — 172.16.0.0/12 (172.16.0.0–172.31.255.255, ~1 million addresses). Class C — 192.168.0.0/16 (192.168.0.0–192.168.255.255, ~65,000 addresses). These are used in home networks, corporate intranets, and are translated to public IPs via NAT (Network Address Translation) when accessing the internet.
What is the difference between /24 and /25?
A /24 gives you 256 IP addresses (254 usable). A /25 splits that network in half — each half has 128 IPs (126 usable). Each time you increase the prefix by 1, you halve the number of hosts. Going from /24 to /25 doubles the number of subnets from 1 to 2, but cuts hosts in half. This is called "subnetting": borrowing bits from the host portion to create more, smaller networks. Common in enterprise networks to isolate departments.