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IP Subnet Calculator
Divide an IPv4 network into equal subnets or use VLSM to allocate subnets by host requirement.
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About this tool
Enter any IPv4 CIDR network (e.g. 192.168.0.0/16) and specify either the number of subnets you need or the required hosts per subnet; the calculator determines the optimal prefix length and lists every resulting subnet with its network address, broadcast address, usable host range, and subnet mask. The VLSM (Variable Length Subnet Masking) mode lets you name multiple sub-networks and specify each one's host requirement — subnets are then allocated from largest to smallest for maximum efficiency. An ASCII-art tree diagram visualises how the address space is carved up.
How to use
- 1 Enter the base network in CIDR notation (e.g. 10.0.0.0/8) in the Network field.
- 2 Choose 'Equal Subnets' mode and enter either the number of subnets or hosts per subnet — the other value is calculated automatically.
- 3 Or switch to 'VLSM' mode, add each subnet by name and required host count, then click 'Calculate'.
- 4 Review the subnet table and ASCII tree diagram; copy any value by clicking on it.
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