IP / CIDR Calculator

Calculate IPv4 and IPv6 boundaries, compare intersections, and aggregate subnets

All input is processed in this browser and is never sent to a server or written to local storage.

Enter an IPv4 or IPv6 CIDR to calculate.

Subnet comparison

Compare containment and intersection of two IPv4 or IPv6 subnets; a single IP is treated as a host address.

Enter two subnets or IP addresses to check containment and intersection.

Subnet aggregation

Enter one IPv4 or IPv6 CIDR or IP per line; merge overlapping and adjacent ranges into the shortest list.

Enter one CIDR or IP per line, then aggregate.

Up to 1,000 entries and 128 KiB; blank lines are ignored; IPv4 and IPv6 are aggregated separately.

Calculation notes

/31 and /32

Usable addresses follow point-to-point and single-host semantics instead of always subtracting network and broadcast addresses.

IPv6 capacity

BigInt preserves the exact address count without floating-point loss.

Address classification

Distinguishes public, private, loopback, link-local, multicast, documentation, and other reserved ranges.

Calculate CIDR boundaries, address counts, and overlap

Enter an IPv4 or IPv6 address with a prefix to calculate its normalized form, network range, and address count. You can also compare two ranges or aggregate a list. The tool applies a prefix mask to address bits; it does not send probes to the network.

Read the CIDR result

The prefix tells how many bits belong to the network. An IPv4 `/24` leaves 8 host bits, for 256 addresses. The tool normalizes an address with host bits set to the range boundaries; the sample spans 192.168.1.0 through 192.168.1.255.

For IPv4 prefixes `/0` through `/30`, the tool follows the traditional subnet convention and subtracts the network and broadcast addresses when calculating first/last usable hosts and usable count. `/31` and `/32` do not subtract those addresses. IPv6 shows its range and total count, with no IPv4-style broadcast or usable-host count.

Input: 192.168.1.25/24
Network: 192.168.1.0
End: 192.168.1.255
First host: 192.168.1.1
Last host: 192.168.1.254
Address count: 256
Usable IPv4 hosts: 254

Compare and aggregate for different tasks

Comparison reports whether two ranges are equal, one contains the other, they are disjoint, or their address families differ. It also shows the intersection and its address count. If a prefix is omitted, comparison treats a single address as `/32` or `/128`; the single-range calculator requires an explicit prefix.

Aggregation accepts one IP or CIDR per line and combines adjacent or overlapping ranges of the same family into a compact CIDR list. The result describes the set of addresses in your input; it does not renumber networks or decide whether the ranges belong together operationally.

Input errors and special cases

IPv4 must contain four decimal octets from 0 to 255; octets with extra leading zeros are rejected. Prefixes must be between 0–32 for IPv4 or 0–128 for IPv6. IPv6 supports `::` compression but rejects a zone identifier beginning with `%`.

Subnet boundaries do not prove that a server is online. `network` and `end` come from bitwise range calculation, while first and last usable hosts follow common IPv4 rules. Actual device counts, routing, reserved-address policies, and cloud-provider restrictions can differ, especially for small or special-purpose ranges.

Local calculation is not network verification

Calculation, comparison, and aggregation run in the current browser; an IP list is not uploaded. Bulk aggregation accepts up to 1,000 lines and 128 KiB. Comparison inputs are limited to 128 characters. Very large ranges are shown as counts rather than enumerated address by address.

The category label uses address-range rules built into the code, such as private, loopback, and documentation ranges. It is not a substitute for a current IANA registry lookup and does not verify routing, reachability, open ports, ownership, or firewall rules. Use the network checker for connection details or DNS lookup for name records.