Subnet / CIDR Calculator
Calculate the network, broadcast, mask, wildcard and usable host range for any IPv4 CIDR — instantly in your browser. Free.
Subnet / CIDR calculator
Enter an IPv4 address with a prefix (10.0.0.5/24), an IP and mask, or a bare IP.
What this subnet calculator does
Common use cases
- 1Planning an IP address scheme
- 2Splitting a network into subnets
- 3Configuring a router or firewall
- 4Checking which subnet an IP is in
- 5Sizing a subnet for N hosts
- 6Learning CIDR and subnetting
Related tools
About subnetting and CIDR
CIDR notation writes a network as an address plus a prefix length, like 10.0.0.0/24 — the prefix says how many leading bits are the network portion. The remaining host bits determine how many addresses the subnet holds.
This calculator derives the network and broadcast addresses, the subnet and wildcard masks, and the usable host range using exact 32-bit math in your browser. The usable count excludes the network and broadcast addresses (except for /31 and /32, which follow their own conventions).
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Got Questions? We Have Answers.
What input does it accept?
CIDR notation like 10.0.0.5/24, an IP with a subnet mask, or a bare IP address (treated as /32).
What does it calculate?
The network and broadcast addresses, subnet and wildcard masks, first and last usable host, total and usable host counts, and the address class and type.
Why is the usable count two less than the total?
The network and broadcast addresses can't be assigned to hosts, so a /24 has 256 total but 254 usable. /31 and /32 are special cases and are handled correctly.
Does it run in my browser?
Yes. All the math is done locally with exact 32-bit operations — nothing is sent anywhere.