ChistStudioWho uses a subnet calculator?
Network engineers planning VLAN allocations, system administrators sizing DHCP scopes, security engineers auditing segmentation, DevOps engineers writing infrastructure-as-code CIDR blocks, and students learning networking fundamentals all rely on this same calculation, done many times a day.
What is subnetting?
Subnetting divides one large IP network into smaller, more manageable pieces by borrowing bits from the host portion of an address to extend the network portion. Every IPv4 address splits into a network part (which subnet it's in) and a host part (which device within that subnet) — subnetting just moves where that split happens.
Common CIDR prefixes at a glance
What this tool calculates
A subnet calculator takes an IPv4 address written in CIDR notation — for example 192.168.1.0/24 — and works out every other address that matters for that network: the network address itself, the broadcast address, the range of addresses that can actually be assigned to devices, and the subnet mask in both dotted-decimal and wildcard form.
Why this matters when designing a network
Every time you split a network into smaller subnets — for VLANs, for separating a guest network from an internal one, or for allocating address blocks to different offices — you need to know exactly where one subnet ends and the next begins, and how many usable host addresses you're left with. Getting this wrong by even one bit means overlapping ranges or wasted address space, both of which cause real outages.
Reading the result
- Network address — identifies the subnet itself and is never assigned to a device.
- Broadcast address — the last address in the range, reserved for sending to every host on the subnet at once.
- Usable host range — every address between the network and broadcast address, available to assign to devices.
- Subnet mask / wildcard mask — the mask defines which bits are network bits; the wildcard mask is its inverse, used in access control list configuration on Cisco-style devices.
Frequently asked questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation combines an IP address with a slash and a number, such as 192.168.1.0/24. The number after the slash indicates how many bits of the address are fixed as the network portion; the rest identifies individual hosts within that network.
How do I calculate the number of usable hosts in a subnet?
Usable hosts equal 2 raised to the power of the number of host bits, minus 2 — one address is reserved for the network identifier and one for the broadcast address. A /24 network has 8 host bits, giving 256 total addresses and 254 usable host addresses.
What is the difference between a network address and a broadcast address?
The network address is the first address in a subnet and identifies the subnet itself; it cannot be assigned to a device. The broadcast address is the last address in the subnet and is used to reach every device on that subnet at once; it also cannot be assigned individually.
What is a /31 or /32 subnet used for?
A /32 identifies a single host with no room for a network or broadcast address — commonly used for loopback addresses or specific host routes. A /31 (RFC 3021) is used for point-to-point router links, treating both addresses as usable since a two-host link has no meaningful broadcast address.