Subnet Calculator
Calculate the network address, broadcast address, usable host range, and subnet mask for any IPv4 CIDR block — free, private, no upload required.
Subnet Calculator computes the network address, broadcast address, subnet mask, wildcard mask, usable host range, and total address count for any IPv4 address and CIDR prefix, plus the IP address type and a full CIDR quick-reference table. Everything runs locally in your browser — nothing is ever sent to a server. Built by FreeToolHub.
CIDR quick reference
| CIDR | Subnet mask | Usable hosts |
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Frequently Asked Questions
What is a subnet mask?
A subnet mask is a 32-bit value that splits an IPv4 address into a network portion and a host portion. Bits set to 1 mark the network portion; bits set to 0 mark the host portion. It is usually written in dotted-decimal form (like 255.255.255.0) or as a CIDR prefix length (like /24).
How is the network address calculated?
The network address is found by performing a bitwise AND between the IP address and the subnet mask. This clears every host bit to 0 while keeping the network bits unchanged, giving the lowest address in the block.
What is the difference between /31 and /32?
A /32 identifies exactly one host with no network or broadcast address, commonly used for host routes or loopback interfaces. A /31 contains exactly two addresses; per RFC 3021 both are treated as usable host addresses (no dedicated network or broadcast address), which is common on point-to-point router links.
What are private IP address ranges?
RFC 1918 reserves three ranges for private networks that are never routed on the public internet: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. This tool also flags loopback (127.0.0.0/8), link-local (169.254.0.0/16), multicast (224.0.0.0/4), and other reserved ranges.
Is my IP address sent to a server?
No. All subnet math runs locally in your browser with plain JavaScript. The IP address and prefix you enter are never sent to any server, logged, or stored.
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation appends a slash and a number to an IP address, like 192.168.1.0/24, where the number is the count of leading 1 bits in the subnet mask. It replaced the older fixed Class A/B/C system and lets networks be sized to any power-of-two boundary.