Subnetting turns an IPv4 address block into smaller networks that are easier to route, secure and manage. This free subnet calculator accepts an IPv4 address in CIDR notation and returns the network address, subnet mask, wildcard mask, broadcast address, host range and address counts.
Try an address such as 192.168.10.34/24. The calculator runs in your browser and does not send the address to an external service.
Calculate an IPv4 subnet
Enter four decimal octets followed by a slash and prefix length. IPv4 prefixes range from /0 to /32.
Free networking tool
IPv4 subnet calculator
Enter an IPv4 address and CIDR prefix to find its subnet boundaries and usable host range.
How to read the subnet results
The network address is the first address in the block after the host bits are set to zero. Routers use the network and prefix together, such as 192.168.10.0/24, to describe the whole range.
The subnet mask shows the same boundary in dotted-decimal form. A /24 uses 24 one-bits followed by eight zero-bits, producing 255.255.255.0. The wildcard mask is the bitwise inverse of the subnet mask and is often used in network-device rules.
For a conventional /0 through /30 subnet, the broadcast address is the last address in the block. The first usable host follows the network address, and the last usable host precedes the broadcast address. The calculator handles /31 and /32 separately because those prefixes have different operational uses.
IPv4 CIDR notation explained
An IPv4 address contains 32 bits. In CIDR notation, the number after the slash states how many leading bits form the network prefix. The remaining bits identify positions inside that block. A longer prefix creates a smaller block: a /24 contains 256 addresses, a /25 contains 128 and a /26 contains 64.
The number of addresses in a block is 2^(32 - prefix). Conventional subnetting removes the network and broadcast addresses from the usable-host count, so a /24 normally has 254 usable host addresses. Requirements vary by platform and topology, so confirm the intended configuration before assigning addresses.
Worked example: 192.168.10.34/27
A /27 leaves five host bits, producing blocks of 32 addresses. In the final octet, those blocks begin at 0, 32, 64, 96 and continue in steps of 32. The address 192.168.10.34 therefore falls inside the block from 192.168.10.32 through 192.168.10.63.
- Network: 192.168.10.32/27
- Subnet mask: 255.255.255.224
- Broadcast: 192.168.10.63
- Usable range: 192.168.10.33–192.168.10.62
- Usable hosts: 30
What is special about /31 and /32?
A /31 contains two addresses. RFC 3021 allows both to identify endpoints on a point-to-point link, where a directed broadcast is unnecessary. Do not assume that a /31 is appropriate for an ordinary multi-access LAN; both ends and the network design must support the point-to-point use.
A /32 contains one address. It commonly represents a host route or a single interface address. Because there is no separate range inside the prefix, the calculator reports the same address as the network and usable host and marks broadcast as not applicable.
Private IPv4 address ranges
RFC 1918 reserves three blocks for private internets: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. These addresses are widely used inside homes, labs and organizations and are not globally routed as ordinary public addresses. The calculator identifies whether the entered address belongs to one of those three ranges.
“Not private” does not automatically mean that an address is safe to use publicly. IPv4 includes other special-purpose ranges, and public address allocation belongs to network operators and registries.
Subnetting skills for networking careers
Subnet calculations appear in network support, cloud operations, security engineering and certification exams. Practice connecting the numerical result to a design decision: estimate the required hosts, leave room for growth, separate trust zones and document the prefix assigned to each segment.
- Estimate how many addresses the segment needs.
- Choose the smallest suitable prefix with reasonable growth capacity.
- Check that proposed subnets do not overlap.
- Reserve gateways and infrastructure addresses according to your standards.
- Record the network, mask, usable range and purpose in the source of truth.
Frequently asked questions
How many usable hosts are in a /24?
A conventional IPv4 /24 has 256 total addresses and 254 usable host addresses after excluding the network and broadcast addresses.
What subnet mask is /26?
A /26 corresponds to 255.255.255.192. It creates blocks of 64 total addresses, normally with 62 usable host addresses.
Is CIDR the same as a subnet mask?
They express the same prefix boundary in different forms. A CIDR prefix such as /24 gives the number of leading network bits; a dotted-decimal subnet mask such as 255.255.255.0 shows those bits by octet.
Does this calculator support IPv6?
No. This tool is deliberately limited to 32-bit IPv4 addresses. IPv6 uses 128-bit addresses and different conventions for subnet planning.
Use the result as a planning check
CIDR makes the network boundary explicit and supports flexible power-of-two blocks, as described in RFC 4632. Use this calculator to check arithmetic, then validate the result against your router, cloud platform and organization’s addressing plan before making a production change.
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