← Infra Atlas · Calculators

Cross-Cloud Subnet Calculator.

A /24 is not a /24 everywhere. AWS, Azure, GCP and OCI each carve reserved IPs out of every subnet — different counts, different positions. Pick a CIDR and see the actual usable host count, side by side, with the rules sourced.

Enter an IPv4 or IPv6 network with its prefix length.
Where these numbers come from
methodSubnet arithmetic — pure CIDR math (RFC 4632 for IPv4, RFC 4291 for IPv6), computed in your browser; no external data involved
curatedReserved-IP rules per cloud — hand-verified against each vendor's VPC/VNet/VCN documentation (verified 2026-05-19); the source link sits under every provider card
Spotted a wrong number? Report it — the issue arrives prefilled →
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Usable here means routable for workloads. AWS and Azure each reserve first 4 + last 1; GCP reserves first 2 + last 2; OCI reserves first 2 + last 1. IPv6 subnets are /64 almost everywhere — the host count is meaningless at that size (~18 quintillion), so the panel shows the prefix you get and the reservations that still apply. Built on the cross-cloud Networking Matrix.