What is CIDR (Classless Inter-Domain Routing)?

CIDR is a method for allocating IP addresses and routing Internet Protocol packets. It replaced the older 'classful' network system (Class A, B, C) to allow for more flexible allocation of IP address blocks. CIDR notation represents an IP address and its associated network mask, written as 'xxx.xxx.xxx.xxx/n', where 'n' is the number of '1' bits in the subnet mask.

Why is the Wildcard Mask useful?

The wildcard mask is the inverse of the subnet mask. It is primarily used in Access Control Lists (ACLs) on routers and firewalls. It tells the device which parts of an IP address to match. A '0' in the wildcard mask means 'match this octet exactly,' while a '255' means 'ignore this octet.'

What's the difference between Total Hosts and Usable Hosts?

Total Hosts is the total number of IP addresses within a subnet, calculated as 2^(32-n). Usable Hosts is the number of addresses that can be assigned to devices. This is typically Total Hosts minus 2, because the first IP is reserved for the Network Address and the last IP is reserved for the Broadcast Address.

What does a /32 mask mean?

A /32 mask (255.255.255.255) specifies a single, exact IP address. The network has only one IP, which is the host address itself. There are no separate network or broadcast addresses in this context, and it has 0 usable hosts.

Can I use this calculator for IPv6?

No, this calculator is designed specifically for IPv4 addresses and CIDR notation. IPv6 uses a different addressing system (128 bits) and notation.

CIDR Calculator - Calculate Subnet, Range & IP Details

Instantly calculate IP address range, subnet mask, wildcard mask, network address, and broadcast address from any IP/CIDR notation. A complete CIDR tool.

CIDR Input

Enter an IPv4 address along with its CIDR mask.

IP / CIDR

Network Address

—

Input IP: —
CIDR Mask: —
Subnet Mask: —
Wildcard Mask: —
Broadcast Address: —
First Host: —
Last Host: —
Total Hosts: —
Usable Hosts: —

How to Use This Calculator

Type a complete IPv4 address in standard dotted decimal format followed by its CIDR mask (e.g., 192.168.1.1/24). Click Calculate to decode the network details: subnet mask, wildcard mask, network/broadcast addresses, host range, and totals. Results populate instantly and can be refreshed as soon as you change the input.

Enter the IP address and CIDR mask (the form matches RFC 4632 formatting).
Validate the IPv4 segments (each octet must stay between 0 and 255) and ensure the mask is between 0 and 32.
Press Calculate or rely on the debounced input listener for fast updates.
Review the highlighted network address and detailed results below.

Methodology

The calculator converts the supplied IP address into a 32-bit integer, applies the mask to derive the network and broadcast addresses using bitwise operations, and computes host totals as 2^(32 - mask). The wildcard mask is the inverse of the subnet mask, and usable host space subtracts the reserved network and broadcast addresses (except for /31 and /32 networks per RFC 3021 recommendations).

Decimal values display with consistent US number formatting to avoid NaN/Infinity artifacts, and any invalid input triggers a friendly error message instead.

Binary breakdown reveals how each octet contributes to the subnet, network, and broadcast representations.
The CSV download mirror the main results so you can archive or share the decoded ranges.
All logic runs in vanilla JavaScript without third-party math libraries, preserving deterministic rounding.

Note: Figures reflect standard IPv4 math; consult RFC 4632 or a network engineer for production planning or IPv6 conversions.

Full original guide (expanded)

The legacy CIDR page bundled navigation lists, related tools, and support links that remain valuable. The sections below preserve that full context for reference.

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Formulas

Network Address

Network = IP Address (long) AND Subnet Mask (long)

Wildcard Mask

Wildcard = NOT Subnet Mask

Broadcast Address

Broadcast = Network Address OR Wildcard Mask

Total Hosts

Total Hosts = 2^(32 - CIDR Mask)

Usable Hosts

Usable Hosts = Total Hosts - 2 (zero when mask ≥ 31)

Citations

Home — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/

Lifestyle Everyday — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/lifestyle-everyday

Miscellaneous — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/subcategories/miscellaneous

RFC 4632 — datatracker.ietf.org · Accessed 2026-01-19
https://datatracker.ietf.org/doc/html/rfc4632

Subnet Calculator (Advanced) — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/subnet-calculator

Changelog

Version: 0.1.0-draft

Last code update: 2026-01-19

Initial audit spec draft generated from HTML extraction (review required).
Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
Confirm sources are authoritative and relevant to the calculator methodology.

✓ Verified by Ugo Candido Last Updated: 2026-01-19 Version 0.1.0-draft

Version 1.5.0