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Subnet & CIDR Calculator: IP Ranges, Masks, Hosts

Enter an IPv4 address and CIDR prefix to get the network, broadcast, usable host range, subnet mask, wildcard, and host count — plus split a block into subnets.

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Usable hosts is total addresses minus the network and broadcast addresses (2(32−prefix) − 2), except a /31 (2 usable, point-to-point per RFC 3021) and a /32 (a single host). All math runs locally in your browser.

How to use this calculator

Type an IPv4 address and choose a CIDR prefix (the /24 part). The calculator instantly shows the network address, broadcast address, the usable host range, total and usable host counts, the subnet mask, and the wildcard mask — and tells you whether the address is private, public, or special-use. To plan VLANs or segments, set a longer split prefix and it lists every child subnet.

Everything runs in your browser; nothing is sent anywhere. The result is encoded in the URL, so you can copy a link to a specific calculation.

What CIDR notation actually means

CIDR (Classless Inter-Domain Routing) describes a network by how many leading bits are fixed. /24 means the first 24 of 32 bits are the network, leaving 8 for hosts — 256 addresses, 254 usable. Each extra bit halves the block: /25 = 128, /26 = 64, /27 = 32. It replaced the rigid Class A/B/C system, so you size a network to what you need instead of jumping in huge steps.

The two addresses you never assign to a device are the network address (first, all host bits 0) and the broadcast address (last, all host bits 1) — which is why usable hosts is total minus 2 (except /31 point-to-point links and /32 single hosts).

Private vs. public ranges

RangeCIDRUse
10.0.0.0 – 10.255.255.25510.0.0.0/8Private (RFC 1918)
172.16.0.0 – 172.31.255.255172.16.0.0/12Private (RFC 1918)
192.168.0.0 – 192.168.255.255192.168.0.0/16Private (RFC 1918)
100.64.0.0 – 100.127.255.255100.64.0.0/10Carrier-grade NAT
169.254.0.0 – 169.254.255.255169.254.0.0/16Link-local (APIPA)
127.0.0.0 – 127.255.255.255127.0.0.0/8Loopback

Home and homelab networks live in the RFC 1918 ranges — most consumer routers default to a 192.168.x.0/24. If you’re segmenting a homelab into VLANs, the split feature above makes carving a /24 into per-VLAN /26s or /27s straightforward.

What this pairs with

Planning the physical side of the network too? The PoE power budget calculator sizes a switch for your APs and cameras, the Wi-Fi 7 homelab guide covers the wireless layer, and the budget networking gear guide rounds up switches and routers worth buying.

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Frequently asked questions

What does a CIDR prefix like /24 mean?
The number after the slash is how many bits, counting from the left, are fixed as the network portion of the address. A /24 fixes the first 24 bits, leaving 8 bits for hosts — that’s the familiar 255.255.255.0 mask with 256 addresses (254 usable). Every bit you add to the prefix halves the network: a /25 is 128 addresses, a /26 is 64, and so on. CIDR (Classless Inter-Domain Routing) replaced the old A/B/C classes so any prefix length is valid.
How many hosts are in a subnet?
Total addresses = 2 to the power of (32 minus the prefix). Usable hosts are normally that minus 2, because the first address is the network identifier and the last is the broadcast address. So a /24 has 256 total and 254 usable; a /26 has 64 and 62; a /30 has 4 and 2. Two exceptions: a /31 has 2 usable addresses (point-to-point links per RFC 3021, no network/broadcast), and a /32 is a single host.
What is the difference between the network and broadcast address?
The network address is the first address in the block (all host bits 0) and identifies the subnet itself — you don’t assign it to a device. The broadcast address is the last address (all host bits 1) and is used to reach every host on the subnet at once. Everything in between is the usable host range you assign to devices. For 192.168.1.0/24 the network is 192.168.1.0, the broadcast is 192.168.1.255, and usable hosts are .1 through .254.
What is a wildcard mask versus a subnet mask?
They’re bitwise inverses. A subnet mask has 1s for the network bits (255.255.255.0 for a /24); a wildcard mask flips them to 0s for network and 1s for host (0.0.0.255 for a /24). Subnet masks are used in interface and routing configuration; wildcard masks appear in access control lists (ACLs) and OSPF on Cisco-style gear, where a 0 means ‘must match’ and a 1 means ‘don’t care.’ This calculator shows both.
What are the private IP address ranges?
RFC 1918 reserves three private ranges that aren’t routed on the public internet: 10.0.0.0/8 (10.x.x.x), 172.16.0.0/12 (172.16.x.x–172.31.x.x), and 192.168.0.0/16 (192.168.x.x). A few others are special-use: 100.64.0.0/10 is carrier-grade NAT, 169.254.0.0/16 is link-local (APIPA), and 127.0.0.0/8 is loopback. This calculator flags whether the address you enter falls in a private, special, or public range.
How do I split a network into smaller subnets?
Pick a longer prefix than the parent block and the network divides into equal pieces. Going from a /24 to /26 splits one 256-address block into four 64-address subnets; /24 to /27 gives eight /27s of 32 addresses each. The number of resulting subnets is 2 to the power of (new prefix minus old prefix). This tool’s ‘split into’ option lists each child subnet’s network, broadcast, and usable range so you can plan VLANs or segments.