IP Range to CIDR Converter

Last reviewed: May 2026

Give it a start and end address and it returns the smallest set of CIDR blocks that covers the range exactly — no extra addresses included, none missed. This is the conversion you need when a vendor, ticket, or allow-list gives you a range but your firewall, ACL, or security group only accepts CIDR.

Start IP

End IP

Try: Exactly one /24 Awkward range RFC 1918 middle block

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Why one range often needs several CIDR blocks

A CIDR block has two hard constraints: it must contain a power-of-two number of addresses, and it must start on an address that is a multiple of that size. A range handed to you by a person respects neither.

Take 10.0.0.5 – 10.0.3.200. It starts five addresses into a /24 and stops partway through another, so no single block can describe it. The converter walks the range greedily — at each step taking the largest block that both starts on a valid boundary and stays inside the range — which is provably the minimal set.

Where this is used day to day

Firewall and ACL rules — most enforcement points accept CIDR or wildcard masks, not arbitrary ranges.
AWS security groups and NACLs — every source and destination field is CIDR-only.
Vendor allow-lists — a supplier sends "we egress from 203.0.113.17 to 203.0.113.94" and you need blocks.
BGP prefix lists and route filters — ranges must become prefixes before they can be advertised or filtered.
DHCP scope migration — converting a legacy pool range into modern CIDR-based definitions.

Common ranges and their CIDR equivalents

Range	CIDR blocks	Notes
192.168.1.0 – 192.168.1.255	`192.168.1.0/24`	Clean single block
10.0.0.0 – 10.255.255.255	`10.0.0.0/8`	RFC 1918 class A
172.16.0.0 – 172.31.255.255	`172.16.0.0/12`	RFC 1918 middle block
192.168.1.1 – 192.168.1.254	`/32` + `/31` + … + `/32`	Excluding network and broadcast fragments it heavily
10.0.0.0 – 10.0.0.1	`10.0.0.0/31`	Point-to-point link (RFC 3021)

That fourth row is worth internalising: trimming a single address off each end of a clean /24 turns one block into more than a dozen. If a range looks like it should be simple but produces many blocks, check whether it has been trimmed at the edges.

Frequently Asked Questions

How do I convert an IP range to CIDR notation?

Start at the first address and repeatedly take the largest CIDR block that is aligned to that address and does not extend past the end address. Move to the address after that block and repeat until the end is reached. Most ranges cannot be expressed as a single CIDR, so the result is usually a set of blocks.

Why does my IP range need more than one CIDR block?

A CIDR block must start on an address that is a multiple of its own size and must contain a power-of-two number of addresses. A range like 10.0.0.5 to 10.0.3.200 starts and ends off those boundaries, so it can only be covered exactly by combining several differently sized blocks.

What is the CIDR for 192.168.1.0 to 192.168.1.255?

That range is exactly 192.168.1.0/24. It starts on a 256-address boundary and contains exactly 256 addresses, so it maps to a single CIDR block with no remainder.