What CIDR prefix lengths are valid?

Valid IPv4 CIDR prefixes run from /0 (the entire Internet, 0.0.0.0/0) to /32 (a single host). Prefixes /31 and /32 have special meanings: /31 has no network or broadcast address (used for point-to-point links per RFC 3021), and /32 identifies a single host route.

Can I enter a subnet mask instead of a prefix length?

Yes. Type the subnet mask in dotted-decimal form (e.g. 255.255.255.0) in the mask field and the tool converts it to the equivalent CIDR prefix and performs the calculation. The mask must be a valid contiguous-bit mask.

How is the IP class determined?

IP classes are determined by the leading bits of the first octet: Class A (1–126), Class B (128–191), Class C (192–223), Class D (224–239, multicast), Class E (240–255, reserved). The loopback range 127.x.x.x is noted separately.

Why are the usable hosts two fewer than total hosts?

The first address in a subnet is the network address (all host bits zero) and the last address is the broadcast address (all host bits one). Both are reserved and cannot be assigned to hosts, leaving total hosts minus 2 usable addresses. Exceptions apply to /31 and /32 subnets.

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IP / CIDR Network Calculator

Enter an IPv4 address with a CIDR prefix or subnet mask to calculate network address, broadcast, host range, wildcard, and binary breakdown.

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About this tool

Input an IPv4 address and either a CIDR prefix length (e.g. /24) or a dotted-decimal subnet mask (e.g. 255.255.255.0). The tool instantly calculates the network address, broadcast address, first and last usable host, total host count, usable host count, subnet mask, wildcard mask, and IP class (A through E). A binary table shows all four octets of the IP, network address, subnet mask, and broadcast address aligned in 8-bit groups so you can see exactly which bits define the network and host portions.

How to use

1 Enter an IPv4 address in the first field (e.g. 192.168.1.0).
2 Enter the CIDR prefix length (e.g. 24) or a dotted-decimal subnet mask (e.g. 255.255.255.0).
3 Click Calculate (or press Enter) to see the full network breakdown.
4 Review the binary table at the bottom to visualize the network and host bit boundaries.

Frequently Asked Questions

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