Azure VNet
Plan Azure virtual network and subnet address ranges accounting for Azure-reserved addresses.
About Azure VNet
Azure VNets, like AWS VPCs, reserve 5 IP addresses in every subnet: the network address, a default gateway address, two addresses reserved for mapping Azure DNS, and the broadcast address. Azure supports VNet address spaces considerably larger than AWS's /16 cap (down to /8 in principle, though most real deployments use /16 to /24), and subnets delegated to platform services like App Service Environments, Azure NetApp Files, or Azure Container Instances typically need a larger minimum subnet size (often /24 or larger) to leave room for the service's own scale-out address consumption.
Formula
Usable IPs per Azure subnet
usable = 2^(32 − subnet_prefix) − 5
Worked example
With the default values below, Azure VNet returns Max Subnets of This Size of 256. Change any input above and every figure here is recalculated in your browser.
Inputs used
- VNet Address Space Prefixaccepts 8–29 /
- 16 /
- Subnet Prefixaccepts 8–29 /
- 24 /
- Subnets Requiring Delegationminimum 0
- 1
Results
- Max Subnets of This Size
- 256
- Usable IPs per Subnet
- 251
- Total VNet Address Space
- 65,536
- Reserved IPs per Subnet (Azure)
- 5
Step by step
- 1Values used
- 2Usable IPs per Azure subnet
- 3Max Subnets of This Size= 256
- 4Usable IPs per Subnet= 251
- 5Total VNet Address Space= 65,536
- 6Reserved IPs per Subnet (Azure)= 5
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
What are Azure's 5 reserved IPs used for?
The network address (first), the default gateway (second), two addresses reserved to map Azure's DNS servers into the VNet space (third and second-to-last), and the broadcast address (last) — identical in count, though not identical in exact purpose, to AWS's 5 reserved addresses.
Why do delegated subnets need extra room?
Services like Azure App Service Environment or Azure NetApp Files provision their own internal infrastructure IPs within the delegated subnet as they scale, so a too-small subnet can block the service from scaling out or even from being created in the first place.
Can I add more address space to a VNet later?
Yes — unlike some cloud providers, Azure lets you add additional address ranges to an existing VNet after creation, and you can also add/resize subnets as long as the new ranges don't overlap with existing subnets or peered VNets.
Does VNet peering require non-overlapping address spaces?
Yes — two VNets with overlapping IP address ranges cannot be peered together, which is why address space planning across an organization's full set of VNets (and any on-premises RFC 1918 ranges) matters from the start, not just within a single VNet.