Free Cloud Subnet & CIDR Calculator
Most subnet calculators show total IP addresses.
Cloud providers reserve part of every subnet for internal platform services — meaning the number of usable IPs is lower than classic subnet math suggests.
This calculator shows how many IP addresses you can actually use in:
- Azure
- AWS
- Google Cloud
- Generic (traditional networking)
What this subnet calculator computes
Enter an IPv4 CIDR range (for example 10.0.0.0/24) and the tool calculates:
- Network address
- Broadcast address
- Subnet mask (dotted decimal)
- Total IP addresses (
2^(32 - prefix)) - Provider-reserved addresses
- Usable IP addresses
- First and last usable IP
If you need classic subnet math without cloud-specific adjustments, use the
→ CIDR to IP Range Calculator
This makes it easier to plan cloud subnets realistically.
Why cloud subnetting behaves differently
In traditional subnetting:
- Network address → reserved
- Broadcast address → reserved
In cloud environments (Azure, AWS, GCP):
- Additional addresses are reserved for routing
- DNS infrastructure
- Platform services
As a result:
A /27 does not give 30 usable IPs in most cloud environments.
This tool models provider-specific reserved address behavior to show realistic usable IP counts.
Cloud provider reserved IP models
Each provider reserves IPs slightly differently.
Learn more about detailed behavior:
- Azure reserved IP addresses → /learn/azure/
- AWS reserved IP addresses → /learn/aws/
- Google Cloud reserved IP addresses → /learn/gcp/
Note: Some managed services require minimum subnet sizes or dedicated subnets. Always validate specific workload requirements before deployment.
Generic (classic) subnet mode
If you select Generic, the calculator uses traditional subnet math:
/0–/30→ 2 reserved addresses (network + broadcast)/31→ 0 reserved (RFC 3021 point-to-point)/32→ single host
For detailed network ranges, broadcast addresses, and wildcard masks, see the
→ CIDR Range Calculator
Example calculation
/26 subnet in Azure or AWS
- Total IP addresses: 64
- Reserved addresses: 5
- Usable IP addresses: 59
This difference becomes critical when deploying:
- Kubernetes clusters
- Private endpoints
- Application gateways
- Load balancers
Small subnets often fail faster than expected.
Subnet sizing rule of thumb
When planning cloud workloads:
/24→ Safe default when growth is expected/26or/27→ Only for tightly controlled workloads- Leave headroom — re-addressing later is painful
Under-sizing subnets is one of the most common cloud networking mistakes.
FAQ
How Many Usable IPs in Common Subnets?
Below are common IPv4 subnet sizes and their usable host counts in traditional networking (classic mode):
/30→ 2 usable IPs (4 total)/29→ 6 usable IPs (8 total)/28→ 14 usable IPs (16 total)/27→ 30 usable IPs (32 total)/26→ 62 usable IPs (64 total)/25→ 126 usable IPs (128 total)/24→ 254 usable IPs (256 total)/23→ 510 usable IPs (512 total)/22→ 1022 usable IPs (1024 total)
Note: In Azure, AWS, and Google Cloud, five IP addresses are typically reserved per subnet. Always use the calculator above to see cloud-adjusted usable IP counts.
Why does this calculator exist when others already do?
Most subnet calculators show total addresses only.
This tool focuses on usable IPs in cloud environments, where additional addresses are reserved.
Why does /27 not give me 30 usable IPs?
Because cloud providers typically reserve more than just network and broadcast addresses.
With five reserved IPs, a /27 (32 total) usually leaves 27 usable IPs.
Does this validate service-specific subnet requirements?
No. This calculator models general subnet behavior only.
Service-specific constraints (for example AKS, RDS, private endpoints, or gateway services) must be validated separately.
Related Networking Tools
IPv6 and advanced subnet planning tools are planned.
Planning larger environments?
If you’re designing hub-and-spoke networks or multi-VNet/VPC environments, proper subnet sizing is critical before deployment.
Use this tool early in the design phase to avoid painful refactoring later.