Technical calculator
CIDR and Subnet Calculator
Calculate IPv4 network, mask, wildcard, usable range, RFC address type, AWS/Azure/GCP usable hosts, subnet splits, and VLSM plans from one CIDR.
Calculated result
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Results update as you change the inputs.
Methodology and assumptions
Formula: Addresses = 2^(32 − prefix). Network = IP AND mask, broadcast = network OR wildcard (the inverted mask). Usable = total − reserved, where reserved is 2 for standard subnets, 5 on AWS and Azure, and 4 on Google Cloud.
Worked example:192.168.1.42/24 resolves to network 192.168.1.0, mask 255.255.255.0, wildcard 0.0.0.255, broadcast 192.168.1.255, 254 usable standard hosts, or 251 on AWS. Split into /26 it gives four subnets of 62 usable hosts.
Common mistake or edge case:Do not subtract two usable addresses for /31 point-to-point networks: RFC 3021 permits both addresses. Cloud subnets reserve more than two addresses and restrict prefix length (AWS /16–/28, Azure /2–/29, Google Cloud up to /29).
Additional official references:
- RFC 6890 special-purpose IP address registries
- RFC 3021 /31 point-to-point links
- AWS VPC subnet CIDR blocks
- Azure Virtual Network FAQ (reserved addresses)
- Google Cloud VPC subnets (reserved addresses)
Read the supporting guide and worked examples.
Frequently asked questions
Why does a /24 have 256 addresses but only 254 usable?
The first address in the block is the network address and the last is the broadcast address; both are reserved on any prefix of /30 or shorter. /31 and /32 are exceptions handled separately (see the mistake note above).
How many usable IPs does an AWS, Azure, or Google Cloud subnet have?
AWS and Azure reserve five addresses per subnet (the first four and the last), so a /24 has 251 usable. Google Cloud reserves four (network, gateway, second-to-last, broadcast), leaving 252. Choose the platform in the calculator to apply those rules to every table.
What is a wildcard mask?
The bitwise inverse of the subnet mask (0.0.0.255 for a /24). Cisco ACLs and OSPF network statements use it to mark which bits may vary.
What is VLSM?
Variable-length subnet masking gives each subnet only the size it needs. Enter host counts such as web:50, db:10 and the calculator allocates the largest first so every subnet stays aligned to its boundary.
Can I use this for IPv6?
No. This calculator is IPv4-only because the 32-bit arithmetic does not extend to IPv6's 128-bit address space.
Pricing last verified:
Frequently Asked Questions
What does the CIDR and Subnet Calculator calculate?
Calculate IPv4 network, mask, wildcard, usable range, RFC address type, AWS/Azure/GCP usable hosts, subnet splits, and VLSM plans from one CIDR.
How accurate is the CIDR and Subnet Calculator?
It is a planning estimate based on the inputs, formula, assumptions, and sources shown on this page. Actual prices, invoices, taxes, discounts, and outcomes can differ.
Which pricing source does the CIDR and Subnet Calculator use?
The calculator links to RFC 4632 CIDR specification as its official source. The displayed pricing or reference data was last verified on 2026-10-01.
Are calculator inputs saved or sent to analytics?
Inputs are processed in your browser. Calculator values are not included in analytics events.