AWS / Networking

Subnet Prefix Calculator

// How many smaller prefixes fit in a larger CIDR block? Calculate splits, usable IPs, and visualize the breakdown.

Prefix Splitter

/16
/20

All Subnets

Select subnets to export for Terraform below.

# CIDR Network Broadcast HostMin (RFC) HostMax (RFC)

Export

Select subnets from the table above to generate export code.

Quick Reference (Day-to-Day)

Prefix Total IPs Usable Hosts (RFC) Netmask Typical Use

Practical list: This table focuses on commonly used prefixes for day-to-day subnetting. For uncommon prefixes, use the calculator selectors above. AWS note: for VPC subnets (typically /16 to /28), subtract 5 reserved IPs from total.