IP Subnet Calculator
| Network address | |
|---|---|
| Broadcast address | |
| Subnet mask | |
| Wildcard mask | |
| Usable host range | |
| Usable hosts | |
| Total addresses |
Paste a CIDR address (192.168.1.0/24) in one field — no separate IP and subnet-mask dropdown — and get the network, broadcast, and usable host range, with /31 (RFC 3021 point-to-point) and /32 (single host) handled correctly instead of the naive formula that gets both wrong.
How it works
- Paste an IPv4 CIDR address, or drag the prefix slider to adjust it live
- Network, broadcast, subnet mask, wildcard mask, and usable host range appear instantly
- /31 and /32 show an explicit note explaining why they don't follow the usual network/broadcast pattern
Frequently asked questions
How many usable hosts does a /31 have?
The naive formula (2^(32-prefix) - 2) gives 0, but that's wrong — per RFC 3021, a /31 used for a point-to-point link has both addresses usable, since there's no network or broadcast address.
What does /32 mean?
A single host — commonly used for a specific route in a routing table or to identify a loopback interface.
What's CIDR notation?
IP address / prefix length, e.g. 192.168.1.0/24 — a compact way to express both an address and the size of its network in one string.
Is my IP address sent to a server?
No — all calculation happens in your browser.
Related tools
From the blog
Update history
- 2026-08-30 Added: a cover image (an address block subdivided by dashed cut lines into subnets, two router icons joined by a single link line for a point-to-point connection, and a slash mark for CIDR notation) — used as the card thumbnail, social share image, and blog title image.
- 2026-08-30 Launched: live IPv4 CIDR subnet calculator (no button) — single-field CIDR input (no separate IP/mask dropdown), with /31 (RFC 3021 point-to-point) and /32 (single host) handled correctly instead of the naive host-count formula. Entirely client-side.