Calculate a subnet from CIDR notation

How it works

1. 1

   Enter an IPv4 address.

2. 2

   Set the prefix length.

3. 3

   Read the network range, mask and host count.

About the CIDR Calculator

CIDR notation such as 10.0.4.0/22 describes a block of IP addresses, but working out where the block starts and ends, or how many hosts it holds, takes binary arithmetic. This calculator takes an IPv4 address and prefix length and shows the network address, broadcast address, subnet mask, first and last usable host and the number of usable hosts.

What you can do

• Enter any IPv4 address in the block and a prefix from /0 to /32.
• See the network and broadcast addresses for that block.
• Get the dotted subnet mask, such as 255.255.252.0 for /22.
• Read the first and last usable host and the usable host count.

When it works best

• Planning subnets for a VPC, office network or Kubernetes cluster.
• Checking whether two addresses fall inside the same range for a firewall rule or security group.
• Converting between a prefix length and a subnet mask when configuring a router.

Things to know

• The subnet maths is done in your browser, with no lookups sent anywhere.
• Only IPv4 is supported, not IPv6.
• For /31 and /32, every address is counted as usable, following point-to-point practice. Cloud providers often reserve extra addresses in each subnet, so the real number available can be lower.
• To convert a single address octet to binary, use the Number Base Converter.

Frequently asked questions