# CIDR Subnet Calculator

> Calculate network, broadcast, mask, wildcard, and host range for any IPv4 or IPv6 CIDR block. Pure math, runs in your browser.

URL: https://uttir.com/cidr-subnet-calculator
Categories: network-tools, calculators, developer-tools
Privacy: Calculation runs locally in your browser. No network calls.

## About

Paste any IP address with a CIDR prefix (like 192.168.1.0/24 or 2001:db8::/64) and see the network, broadcast, mask, wildcard, and usable host range. Works for both IPv4 and IPv6.

Pure math — no network calls. Useful for planning network ranges, configuring firewalls, or learning subnetting.

## How to use

1. **Type an IP with a prefix** — Format: IP/prefix, e.g. 10.0.0.0/8 or 2001:db8::/32.
2. **Read the result** — Network address, mask, wildcard, broadcast (IPv4), and usable host count are shown. For IPv6, the total address count is shown (it is usually astronomically large).

## FAQ

### What is CIDR?

CIDR (Classless Inter-Domain Routing) is the modern way to write IP address ranges. The number after the slash is the prefix length — how many bits are fixed. 192.168.1.0/24 means the first 24 bits are the network, the last 8 are hosts.

### Why does /31 show only 2 hosts and no broadcast?

RFC 3021 redefined /31 as point-to-point links with no broadcast address — every address is usable. /32 is a single host route. Anything wider (/30 and shorter) reserves 2 addresses for network and broadcast.

### How do I find the subnet of a host?

Replace the host portion with 0s and keep the prefix. For 192.168.1.42/24, the network is 192.168.1.0/24. For 10.5.7.13/16, the network is 10.5.0.0/16. The tool does this automatically when you type any IP — the network is always shown.

### Does this work for IPv6?

Yes. IPv6 prefixes 0–128 are supported. The "total addresses" can be astronomically large (a /64 has 2^64 of them) so it is shown as a raw number rather than a usable-host count.

## Related tools

- [My IP Address](https://uttir.com/my-ip) — See your public IP, approximate location, ISP, and ASN — useful for VPN checks and remote-access setup.
- [IP Geolocation Lookup](https://uttir.com/ip-geolocation-lookup) — Look up geolocation info for any IPv4 or IPv6 address — country, city, ISP, ASN, timezone. Free, runs in your browser.
- [DNS Lookup](https://uttir.com/dns-lookup) — Query DNS records (A, AAAA, MX, TXT, NS, CNAME, SOA, CAA) for any domain using Google DNS-over-HTTPS.
- [WHOIS / RDAP Lookup](https://uttir.com/whois-lookup) — Look up domain or IP registration info via RDAP. Registrar, status, dates, nameservers, contacts. Free, runs in your browser.

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For the full HTML page with the live tool, visit https://uttir.com/cidr-subnet-calculator.
This file is the markdown rendering at https://uttir.com/cidr-subnet-calculator.md. See https://uttir.com/llms.txt for a site-wide summary.