IPv4 Subnet Calculator

Check an IPv4 block

1. Choose CIDR and enter an address with its slash prefix, such as 192.0.2.37/27. Alternatively, choose Address + subnet mask and enter 192.0.2.37 with 255.255.255.224. These are documentation examples, not a suggested live network.
2. Use four decimal octets from 0 to 255 without leading zeros. Prefixes run from /0 to /32; a dotted subnet mask must have contiguous network bits. Each input format retains its own entries when you switch.
3. Calculate, then check the containing network, mask, block range and qualified host interpretation. Copy keeps the input and limitations with the result. Editing an input removes the previous answer.

What the prefix and ranges mean

An IPv4 address contains 32 bits. The number after the slash counts network-prefix bits; the remaining bits determine the size of the block. A /27 leaves five bits, so the block contains 32 addresses. A /24 contains 256, while /32 identifies one address.

The input need not be the block's first address. For 192.0.2.37/27, the containing network is 192.0.2.32/27 and the full range ends at 192.0.2.63. The calculator retains the address you entered instead of silently replacing it with the boundary.

For conventional /0 through /30 arithmetic, the first address is the network boundary and the last is the computed broadcast endpoint; the positions between them give the conventional host count. That range can still include special-purpose addresses and is not a guarantee that each address may be assigned or reached.

A /31 needs different context: RFC 3021 permits both endpoints on an eligible point-to-point link, without a separate subnet-directed broadcast. A /32 is a single-address prefix or host route, not a pool for additional devices. The calculator shows these distinctions rather than subtracting two addresses in every case.

Check a normal block and the edge cases

For 192.0.2.37/27, the mask is 255.255.255.224 and its inverse wildcard is 0.0.0.31. The complete block is 192.0.2.32 through 192.0.2.63, with 30 conventional host positions from 192.0.2.33 through 192.0.2.62. The wildcard is not a subnet-mask input.

Both 203.0.113.6/31 and 203.0.113.7/31 belong to 203.0.113.6/31. Its two addresses are conditional point-to-point endpoints, not automatically usable hosts on an ordinary shared network. For 203.0.113.9/32, the block contains only that one address.

The /0 prefix covers all 4,294,967,296 IPv4 addresses, from 0.0.0.0 through 255.255.255.255. It is also the default-route prefix. This enormous arithmetic block is not one deployable host pool, and the calculator does not generate a list of its addresses.

Address arithmetic is not a network check

A mathematically valid input may be private, reserved, documentation-only or otherwise unsuitable for your intended use. The calculator does not classify every special range, check ownership, test connectivity or decide which addresses your provider or network allows.

Only IPv4 CIDR and contiguous dotted subnet masks are supported. IPv6, hostnames, abbreviated or leading-zero addresses, ACL wildcard input, route aggregation and dividing a block into smaller subnets are outside this tool. Rejected text is not silently repaired or resolved.

Confirm topology, address allocation and device support before configuring a network. The /31 interpretation assumes an eligible point-to-point link; /32 is a one-address route. Counts describe address positions, not available devices, forwarding permission or a security assessment.

Your address calculation

Calculation takes place in your browser. This tool does not add address uploads, DNS lookups, probes, saved inputs or address-bearing share links. Copy writes the summary to your clipboard only when requested, with selected text for manual copying if access is unavailable. Existing site services still follow the site privacy policy.