Azure VNet and subnet calculator
Calculate Azure subnets accounting for Azure's 5 reserved IP addresses and service size requirements.
Enter an address and prefix, e.g. 10.100.1.0/24
Presets:
Runs in your browser. Nothing you type is sent to the server.
About this tool
Microsoft Azure reserves 5 IP addresses in every subnet: the network address (x.0), Azure default gateway router (x.1), two Azure DNS mapping IPs (x.2 and x.3), and the broadcast address (x.255). A /24 subnet yields 251 usable host IPs, not 254. In addition, critical Azure platform services require specific minimum subnet sizes: GatewaySubnet requires at least /27 (/26 recommended), AzureFirewallSubnet and AzureBastionSubnet require /26, and ApplicationGatewaySubnet requires /24. Use this tool to plan address spaces and avoid deployment failures.