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CIDR subnet calculator
Enter an IPv4 CIDR block to see its range and size, and split it into smaller subnets.
Common questions
How many IP addresses does each AWS subnet lose?
AWS reserves 5 addresses in every subnet: the network address, the next three for the VPC router, DNS and future use, and the broadcast address. A /24 subnet gives 251 usable addresses, not 254.
What subnet sizes does AWS allow?
VPC subnets can be between /16 and /28.
What does the prefix length mean?
The number after the slash is how many bits of the address identify the network. A /24 leaves 8 bits for hosts, which is 256 addresses.
Is my input sent anywhere?
No. Everything runs in your browser.