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IP / CIDR calculator

Find network boundaries and exact address counts.

How to use ↓

IPv4: /0–32 · IPv6: /0–128. Domains, ports, zone IDs and dotted-decimal masks are not supported.

CIDR calculations do not look up or connect to an IP, or store or transmit inputs and results. The IP checks below only make requests when you press their buttons.

My public IP

Press the button to read your connection IP and country code from this site's Cloudflare diagnostic response. A VPN or proxy shows its exit IP. Only the IPv4 or IPv6 address used for this connection is shown.

QUICK GUIDE

Find network boundaries with CIDR.

Enter an IP and its prefix length after /. Host bits are cleared to find the network start. Large IPv6 address counts use exact integer arithmetic.

  1. 01

    Enter an address and prefix

    Enter an address such as 192.168.1.10/24 or 2001:db8::1/64. Compressed IPv6 and a trailing IPv4 component are supported.

  2. 02

    Check the range and membership

    Optionally enter an IP of the same address family to check membership. The tool calculates ranges; it never contacts network devices.

  3. 03

    Review the assumptions

    Address counts do not mean assignable or Internet-reachable devices. Check reserved addresses and any extra restrictions imposed by your cloud provider or equipment.

192.168.1.10/24

192.168.1.0/24
255.255.255.0
192.168.1.0 → 192.168.1.255
256 addresses

References: RFC 3021 · RFC 4291 · RFC 5952

Frequently asked questions

How are /31 and /32 handled?

IPv4 /0–30 displays the conventional host range excluding its first and last addresses. /31 assumes two point-to-point endpoints; /32 is one address. Neither displays a separate broadcast address.

Why is there no IPv6 host count?

IPv6 has no broadcast. We show the full address range and count, not a claim about assignable hosts. IPv6 with an embedded IPv4 address is also displayed in compressed hexadecimal form.

Optional · External IP information

IP country and provider lookup — free quota applies

IPWhois allows 1,000 free requests per day shared across this site's domain. The remaining site-wide quota is not provided, and provider policies and availability may change. Prefer the unlimited, offline CIDR calculator above when it meets your needs.

This browser adds a limit of 20 attempts per 24 hours from the first request, spaced at least 10 seconds apart. Failed or canceled attempts count. A quota response blocks requests until the indicated time, or for 24 hours if no readable reset time is available. There are no automatic retries or paid upgrades.

Pressing lookup sends the entered IP and your connection IP and browser information to ipwho.is. Cookies, credentials and the referring page address are omitted. CIDR inputs are never sent automatically.

This does not track an exact address, a person or their movements. Private, local, documentation and other special addresses are excluded. Countries and cities are estimates and can differ from actual locations, especially with VPNs or carrier networks.

IPs and results remain in this page's memory. Only attempt counts and waiting times are stored in localStorage and shared across tabs to prevent excess requests. Results can be reused in this page for 5 minutes. External lookup is disabled if storage or cross-tab locking is unavailable.

IPWhois source and free quota · Privacy notice