Free IP Subnet Calculator
Updated September 2026
Calculate subnet ranges, broadcast addresses, host counts, and IP class from any IPv4 CIDR notation. Free online subnet calculator.
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Calculate subnet ranges, broadcast addresses, host counts, and IP class from any IPv4 CIDR notation. Free online subnet calculator. Results are immediate — no waiting, no loading screens, no account required.
Who uses the Subnet Calculator?
- Network engineers planning IPv4 address allocation for data center or office deployments.
- Students studying for CCNA and network certification exams practicing subnetting.
- System administrators configuring firewall rules and routing policies with correct subnet notation.
Common uses and search terms
The Subnet Calculator is frequently used for: subnet, CIDR, subnet calculator, network. Whether you need a quick result or are working through a longer project, the tool handles all common variations without any configuration.
Why use Allio Tools's Subnet Calculator?
Everything runs locally in your browser. No data is sent to a server, logged, or stored anywhere. The tool is completely free with no usage limits, no premium tiers, and no account required. Available in 11 languages and optimised for all screen sizes, the Subnet Calculator works on desktop, tablet, and mobile with no app download needed.
See also:IP Address Lookup · Website Speed Test · DNS Lookup
How the Subnet Calculator works
Enter an IPv4 address with CIDR prefix length (e.g. 192.168.1.0/24) in the input field.
Click Calculate to instantly see: network address, broadcast address, first/last host, subnet mask, usable host count, IP class, and binary mask.
Results appear in a table below the input.
Change the prefix length and recalculate to compare different subnet sizes for the same network.
Tips & tricks
- This tool is IPv4-only — entering an IPv6 address or prefix returns an 'Invalid IP/prefix' error.
- There's no built-in wildcard mask output or subnet-splitting table — for those, calculate manually from the subnet mask this tool gives you, or use a dedicated Cisco subnetting tool.
- There's no 'are these two IPs in the same subnet' checker — compare the Network Address results for two CIDR entries manually to check.
- The IP Class field (A/B/C) reflects historical classful addressing based on prefix length, not the CIDR-based classless system actually used since the 1990s — treat it as informational only.
Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation expresses an IP address and its subnet mask together: 192.168.1.0/24. The number after / is the prefix length — the count of bits used for the network portion. /24 = 255.255.255.0 mask.
How many usable hosts does a /24 subnet have?
A /24 has 2^8 = 256 addresses total. Subtract 2 (network address and broadcast address) = 254 usable host addresses. Formula: 2^(32-prefix) − 2 usable hosts. This tool computes that automatically for /0 through /32.
What are common subnet sizes?
/30 = 2 hosts (point-to-point links), /29 = 6 hosts, /28 = 14 hosts, /27 = 30 hosts, /26 = 62 hosts, /25 = 126 hosts, /24 = 254 hosts, /23 = 510 hosts, /22 = 1022 hosts.
Does this tool calculate a wildcard mask?
No — it outputs the subnet mask (e.g. 255.255.255.0) but not the inverse wildcard mask used in Cisco ACLs and OSPF configs. To get the wildcard mask, invert each octet of the subnet mask yourself (255 minus each octet).
Does this tool support IPv6 subnetting?
No — this calculator accepts IPv4 addresses only (dotted-decimal format with a /0–/32 prefix). An IPv6 address or prefix will be rejected as invalid input.
Is my data safe when using the Subnet Calculator?
Completely safe. The Subnet Calculator processes everything locally in your browser. No input data, results, or usage information is ever transmitted to or stored on any server.
How current is the data returned by the Subnet Calculator?
The Subnet Calculator fetches live data in real time each time you run it. Results reflect the current state of the server or domain at the moment of the request.
Why does the Subnet Calculator sometimes return different results than other tools?
Results depend on the real-time state of the target server and DNS propagation, which can vary by geographic region and caching TTL. If you see inconsistencies, wait a few minutes and re-test — DNS changes can take up to 48 hours to propagate fully worldwide.
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