Subnet Splitter & CIDR Visualizer
Increasing a CIDR prefix divides a network into equal-size child subnets. Use the visual boundary to understand exactly what happens when a parent block is split into smaller networks.
How subnet splitting works
Every one-bit increase in prefix length halves the address count and doubles the number of equal child subnets. Splitting a /24 into /25 creates two /25 networks; splitting it into /26 creates four /26 networks.
This property makes CIDR hierarchy predictable. A /24 contains 256 addresses, each /25 contains 128, and each /26 contains 64.
Split a /24 into /26 networks
A /24 spans 256 addresses. Moving to /26 borrows two additional network bits, creating 2² = 4 child subnets. Their final-octet boundaries are 0, 64, 128 and 192, and each child contains 64 addresses.
Choosing a child prefix
If you know how many equal subnets you need, choose enough borrowed bits so 2ᵇ is at least that number. If you know how many hosts each subnet needs, choose enough remaining host bits to provide the required address capacity.
Equal subnetting vs VLSM
A simple subnet split creates equal-size child networks. Variable Length Subnet Masking can allocate children of different sizes, which can use address space more efficiently when host requirements vary.
What this calculator shows
The result panel reports the canonical network address, broadcast address, first and last conventional usable addresses, dotted-decimal subnet mask, wildcard mask, total IPv4 address count and usable-host count. The live 32-bit boundary updates with the CIDR prefix, so the relationship between prefix length, block size and address capacity is visible instead of hidden behind a static table.
How to read the result correctly
The calculator normalizes the IP address you enter to the network block that contains it. That means an input such as 192.168.1.42/24 correctly resolves to network 192.168.1.0/24. For prefixes /0 through /30, conventional IPv4 subnetting reserves the first address as the network identifier and the final address as broadcast. /31 and /32 have different practical semantics, so their address counts should not be interpreted with the ordinary “subtract two” rule.
Related subnet tools
You can also use the subnetting cheat sheet for a complete IPv4 prefix reference, browse individual CIDR prefix pages, try the IPv6 subnet calculator, or return to the main visual subnet calculator.
Frequently asked questions
How do I split a subnet?
Increase the CIDR prefix. Each extra prefix bit doubles the number of equal child subnets and halves the size of each child.
How many /26 subnets fit in a /24?
Four /26 subnets fit inside one /24.
How many /28 subnets fit in a /24?
Sixteen /28 subnets fit inside one /24.