IP Subnet Calculator
Turn an IPv4 address and CIDR prefix into the subnet mask, network and broadcast addresses, the usable host range and how many hosts fit — with the private-range and wildcard details.
A CIDR prefix says how many leading bits identify the network: /24 fixes the first 24 bits, leaving 8 for hosts, which gives 256 addresses of which 254 are usable — the first is the network address and the last is the broadcast address.
How the ip subnet calculator works
A CIDR prefix says how many leading bits identify the network: /24 fixes the first 24 bits, leaving 8 for hosts, which gives 256 addresses of which 254 are usable — the first is the network address and the last is the broadcast address. The mask is those leading bits set to 1 (255.255.255.0 for /24). A /31 is the exception: it carries exactly two usable addresses for point-to-point links, and a /32 is a single host.
Formula: addresses = 2^(32 − prefix); usable = addresses − 2 (except /31 and /32)
Worked examples
| Inputs | Usable hosts | Note |
|---|---|---|
| 192.168.1.10/24 | 254 | 254 usable hosts, mask 255.255.255.0 |
| 10.0.0.5/8 | 16,777,214 | 16,777,214 usable hosts |
| A /30 point-to-point link | 2 | 2 usable addresses |
FAQFrequently asked questions
What does /24 mean?
The first 24 bits identify the network, leaving 8 bits for hosts: 256 addresses, 254 of them usable.
Why are two addresses unusable?
The first is the network address and the last is the broadcast address. The exceptions are /31 (two usable, for point-to-point links) and /32 (a single host).
What is a wildcard mask?
The inverse of the subnet mask, used in access-control lists on Cisco and similar equipment — 0.0.0.255 pairs with 255.255.255.0.
Which ranges are private?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, defined in RFC 1918. They are not routed on the public internet.
How do I split a network?
Increase the prefix by one to halve it: a /24 splits into two /25s of 126 usable hosts each.
Where these figures come from
- IEC 80000-13 — Information science and technology (quantities and units) — the decimal (kB, MB) versus binary (KiB, MiB) prefixes used throughout
- RFC 4632 — Classless Inter-domain Routing (CIDR) — the address-plan arithmetic behind the subnet calculator
- RFC 1918 — Address Allocation for Private Internets — the private ranges the subnet calculator recognises
- NIST SP 800-63B — Digital Identity Guidelines, Authentication — length over composition rules; the basis of the password guidance here
- NIST SP 800-57 Part 1 — Recommendation for Key Management — key-strength comparisons used by the key-space calculator
- National Cyber Security Centre — password guidance — UK national guidance on password policy
Last checked: September 2026. Units follow the SI decimal convention (IEC 80000-13 defines the binary alternatives); network and security figures cite the defining standard.