CIDR Calculator
Convert a CIDR prefix to a subnet mask, count addresses and split a network into smaller blocks.
CIDR reference table (/0 – /32)
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) describes an IP address block by address and prefix length, such as 10.0.0.0/22. The prefix says how many bits belong to the network part; the smaller the prefix, the bigger the block.
What the calculator does
- Converts a prefix to a subnet mask (/22 → 255.255.252.0)
- Counts the addresses in the block
- Splits the block into /24, /27 or any size of subnet and lists each one
Cloud and enterprise networks
Splitting CIDR blocks correctly is critical when planning AWS VPCs, Azure VNets and Google Cloud subnets, segmenting office networks or doing IP address management.
How to use CIDR Calculator
- Enter a CIDR block (e.g. 10.0.0.0/22) or a prefix.
- Review the mask and address count.
- Choose the subnet size to split into.
- Copy the resulting subnet list.
Why use this tool?
Prevents overlapping subnets and helps you use address space efficiently.
FAQ
How many /27s fit in a /24?
Eight. Each step in prefix halves the block; /27 is three steps smaller than /24, so 2³ = 8 blocks of 32 addresses.
What does /32 mean?
A single IP address, often used in firewall rules for one host.
Which block is recommended for an AWS VPC?
Private blocks between /16 and /24 are common; leave room to grow.
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