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IP Subnet Calculator

IPv4 CIDR ranges, masks and hosts

By Guga — BrowserTools maintainer, Tbilisi, Georgia Updated 2026-08-16
Free Private No uploads
What is IP Subnet Calculator?

Type an IPv4 address and a prefix length between 0 and 32, and every field of the enclosing block is derived by hand: the network address, the dotted netmask, its bitwise inverse the wildcard, the broadcast address, the first and last usable host, the total address count and the usable host count. The address and the mask are also shown as 32-bit binary with a dot after each octet, which is where the arithmetic stops being magic — the network address is the address ANDed with the mask, and the host bits are simply whatever that AND discards. The /31 and /32 cases follow RFC 3021 rather than the older habit of subtracting two: a /31 reports both addresses as usable for a point-to-point link, and a /32 reports a single address. Chips for the common prefixes sit under the inputs.

Enter an IPv4 address and CIDR prefix (or dotted mask) to get the network address, broadcast, usable host range, wildcard mask, total hosts and binary representation.

Private IP Subnet Calculator In Your Browser

IP Subnet Calculator is processed locally with client-side JavaScript. Your files never touch a server, and there is no queue to wait in.

Step-by-Step

How to use IP Subnet Calculator

1

Enter the IPv4 address in the first field, for example 192.168.1.10.

2

Set the prefix length in the CIDR field between 0 and 32, or press one of the /8, /16, /20, /24, /30 or /32 chips.

3

Read the Network /n panel for the network address, netmask, wildcard mask, broadcast, first host, last host, total addresses and usable hosts.

4

Compare the two binary rows to see which bits of the address survive the AND and which become host bits.

Key Capabilities
  • /31 and /32 follow RFC 3021 — a /31 reports two usable addresses and a /32 reports one — rather than subtracting two from the total.
  • Prefix 0 is supported and yields the whole address space, with a wildcard of 0.0.0.0 and a broadcast of 255.255.255.255.
  • The address and the derived mask are both rendered as dotted 32-bit binary, so the AND that produces the network address can be checked by eye.
  • Bad input is caught before anything is drawn: a malformed address raises its own error, and a prefix outside 0–32 leaves the result panel empty.
Common Use Cases
  • A network engineer writes an ACL entry and needs the wildcard mask and host range that go with a proposed block.
  • A sysadmin splitting 10.0.0.0/8 into departmental /16s checks the broadcast address and usable count before committing the change.
  • A student learning binary arithmetic compares the address and netmask rows to see exactly where the host bits get cut off.
Clear Answers

Frequently Asked Questions

Why does a /31 report two usable hosts?
The traditional reservation of a network address and a broadcast address would leave a 31 with nothing at all. RFC 3021 redefines both as usable for point-to-point links, and a /32 is one address with no reservation whatsoever. The arithmetic here follows that rule rather than the older subtraction.
Can I paste a dotted mask such as 255.255.255.0?
Not directly — the second field takes a prefix length from 0 to 32. Convert by counting the leading one bits: 255.255.255.0 has 24 of them, so 192.168.1.10/24 is the equivalent entry. The netmask you need appears beneath the prefix box as soon as the value is valid.
Where is a wildcard mask actually used?
It is the bitwise inverse of the netmask, and several router and firewall languages accept it in place of a netmask. A rule written with 0.0.0.255 matches any value of the last octet across a /24, which is why wildcards turn up in access lists and in routing protocol configuration.
Does it handle IPv6?
No. The address field takes four dotted decimal octets, so the arithmetic here is IPv4 only. IPv6 works on 128-bit prefixes, where the boundary that actually matters in practice is /64 rather than the familiar /24.