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CIDR Subnet Calculator

Network

Calculate subnet masks, network ranges, usable IPs, and wildcard masks from CIDR notation.

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CIDR Notation

A /24 network sounds like it should provide 256 usable addresses, but two of those, the network address itself and the broadcast address, are reserved and can't actually be assigned to a device, which is exactly the kind of detail that leads to under-provisioning a subnet if the math is done from memory rather than calculated properly. This tool calculates the actual subnet mask, network range, usable IP addresses, and wildcard mask from any CIDR notation, accounting for those reserved addresses rather than a naive total that overstates actual capacity.

See more about the CIDR Subnet Calculator

Useful for sizing a cloud subnet correctly before provisioning it, understanding exactly how many devices a given CIDR block can actually support once reserved addresses are excluded, or checking a network range's boundaries before assigning IP addresses within it.

Key features

  • Clean interface
  • Fast processing
  • No signup required
  • Works offline

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Quick answers for CIDR Subnet Calculator

What does it calculate from a CIDR block?
It calculates the network, subnet mask, wildcard mask, broadcast address, first and last host, total addresses, and usable host count from the IPv4 address and prefix.
Does it handle /31 and /32 subnets correctly?
Yes. /31 reports two usable point-to-point addresses, while /32 reports one address, instead of applying the ordinary network-and-broadcast subtraction.
Do I need to enter the subnet mask separately?
No, entering an address with its CIDR prefix (like 192.168.1.0/24) is enough, the subnet mask and every other value are derived from that prefix automatically.