Why subtract 2 from the host count?

The first address of a subnet is the network address and the last is the broadcast address, and neither can be assigned to a host, so usable hosts are 2^(32-prefix) - 2. Exceptions are /31 (point-to-point links, both usable per RFC 3021) and /32 (a single host).

What is a wildcard mask?

It is the bitwise inverse of the subnet mask (255.255.255.0 becomes 0.0.0.255), used in Cisco ACLs and OSPF where 0 bits must match and 1 bits are ignored.

Which addresses are private?

RFC 1918 private ranges are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. 100.64.0.0/10 is carrier-grade NAT shared space, 127.0.0.0/8 is loopback and 169.254.0.0/16 is link-local.

No. Everything runs locally in your browser with no network upload and is discarded when you close the page, so it is safe for internal or sensitive data.

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🌐IP Subnet Calculator - CIDR, Netmask & Usable Hosts Online

Planning internal networks, firewall rules, cloud security groups or router ACLs means working out exactly which addresses a CIDR block covers. Enter IP/prefix (like 10.0.8.20/22) or "IP netmask" and the tool instantly shows the network and broadcast addresses, the first and last usable hosts, usable and total address counts, the subnet and wildcard masks, the address class (A–E) and whether the address is private, public, loopback, link-local or carrier-grade NAT. A binary view colors network and host bits, and a /0–/32 reference table lets you look up masks and switch prefixes with one click.

Free · No sign-up · Runs in your browserLast updated: 2026-10-26

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How to use Subnet Calculator

1Enter an IP and prefix (e.g. 192.168.1.10/24) or "IP netmask"
2Read the network, broadcast, usable range and host counts
3Switch prefix length via the dropdown or table to compare subnet sizes

FAQ

Why subtract 2 from the host count?: The first address of a subnet is the network address and the last is the broadcast address, and neither can be assigned to a host, so usable hosts are 2^(32-prefix) - 2. Exceptions are /31 (point-to-point links, both usable per RFC 3021) and /32 (a single host).
What is a wildcard mask?: It is the bitwise inverse of the subnet mask (255.255.255.0 becomes 0.0.0.255), used in Cisco ACLs and OSPF where 0 bits must match and 1 bits are ignored.
Which addresses are private?: RFC 1918 private ranges are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. 100.64.0.0/10 is carrier-grade NAT shared space, 127.0.0.0/8 is loopback and 169.254.0.0/16 is link-local.
Is my data uploaded?: No. Everything runs locally in your browser with no network upload and is discarded when you close the page, so it is safe for internal or sensitive data.