← 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.

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.