Subnet & CIDR Calculator: IP Ranges, Masks, Hosts

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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.

Ranges and masks follow the RFCs each result cites.

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.

Worked examples

These are this calculator’s own outputs, computed with the same formula the tool runs in your browser — so you can see a real answer without touching a single input.

The default home/homelab LAN — a consumer router handing out 192.168.1.x. IP 192.168.1.0, prefix /24, no split. (This is exactly the tool’s default state on page load.)

  • Inputs: IPv4 address = 192.168.1.0, Prefix = /24, Split into = (no split)
  • Result: Network address 192.168.1.0/24 | Broadcast address 192.168.1.255 | Usable host range 192.168.1.1 - 192.168.1.254 | Usable hosts 254 (256 total addresses) | Subnet mask 255.255.255.0 | Wildcard mask 0.0.0.255 | Address type Private (RFC 1918 - not internet-routable)

Carving the same home /24 into four VLANs (main, IoT, guest, cameras) — IP 192.168.1.0, prefix /24, split into /26. The dropdown option reads “/26 (4 subnets)”

  • Inputs: IPv4 address = 192.168.1.0, Prefix = /24, Split into = /26
  • Result: Heading “Split /24 into 4 x /26 subnets”, table rows: 1) 192.168.1.0/26, 192.168.1.1-192.168.1.62, bcast 192.168.1.63, 62 hosts. 2) 192.168.1.64/26, 192.168.1.65-192.168.1.126, bcast 192.168.1.127, 62 hosts. 3) 192.168.1.128/26, 192.168.1.129-192.168.1.190, bcast 192.168.1.191, 62 hosts. 4) 192.168.1.192/26, 192.168.1.193-192.168.1.254, bcast 192.168.1.255, 62 hosts. (Cards above still describe the parent /24.)

A homelab host address that is NOT the start of its block — a Proxmox node at 10.0.30.75 on a /22 lab network. Shows that the tool snaps the entered address down to its network address

  • Inputs: IPv4 address = 10.0.30.75, Prefix = /22, Split into = (no split)
  • Result: Network address 10.0.28.0/22 | Broadcast address 10.0.31.255 | Usable host range 10.0.28.1 - 10.0.31.254 | Usable hosts 1,022 (1,024 total addresses) | Subnet mask 255.255.252.0 | Wildcard mask 0.0.3.255 | Address type Private (RFC 1918 - not internet-routable)

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 the child subnets.

The calculation runs in your browser. A copied share link includes the IP address, prefix and split setting. Anyone with that link can read them, and opening it sends those URL settings to the site’s hosting infrastructure. I use site analytics to measure visits and tool interactions. Calculator parameters are removed from Google Analytics page URLs and referrers. See the privacy policy for the data collected.

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
224.0.0.0 – 239.255.255.255224.0.0.0/4Multicast (RFC 5771)
0.0.0.0 – 0.255.255.2550.0.0.0/8“This network” (RFC 791) — not routable
198.18.0.0 – 198.19.255.255198.18.0.0/15Benchmarking (RFC 2544)
192.0.2.0 – 192.0.2.255192.0.2.0/24Documentation, TEST-NET-1 (RFC 5737)
198.51.100.0 – 198.51.100.255198.51.100.0/24Documentation, TEST-NET-2 (RFC 5737)
203.0.113.0 – 203.0.113.255203.0.113.0/24Documentation, TEST-NET-3 (RFC 5737)
240.0.0.0 – 255.255.255.255240.0.0.0/4Reserved (RFC 1112) — not routable; the last address is also the limited broadcast below
255.255.255.255255.255.255.255/32Limited broadcast (RFC 919)

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.

Assumptions and sources

  • The private ranges this tool flags (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are defined in RFC 1918; the carrier-grade NAT range (100.64.0.0/10) is defined in RFC 6598; link-local (169.254.0.0/16) is RFC 3927 and loopback (127.0.0.0/8) is RFC 1122 Section 3.2.1.3.
  • The special-purpose blocks the tool labels - 0.0.0.0/8, 198.18.0.0/15, the three RFC 5737 documentation /24s, 240.0.0.0/4 and 255.255.255.255 - are in the IANA IPv4 Special-Purpose Address Registry, which records each of them as Globally Reachable: False.
  • The multicast range (224.0.0.0/4) is not in that registry - IANA tracks multicast separately, in the IPv4 Multicast Address Space Registry, and assigns it no Globally Reachable value. The block is defined as Class D multicast by RFC 1112 Section 4, with its assignment rules in RFC 5771.
  • The tool flags the blocks listed above and reports anything outside them as public. That is not the whole of the special-purpose registry: 192.0.0.0/24 (IETF Protocol Assignments, RFC 6890) is also Globally Reachable: False and is currently reported as public.
  • The /31 exception - two usable addresses on point-to-point links, with no network/broadcast pair - is per RFC 3021.
  • Everything else (network and broadcast addresses, host counts, masks, wildcard masks, splits) is exact 32-bit arithmetic from those definitions; there are no estimates in this tool.

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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. The dropdown offers splits up to 1,024 subnets, and the results table renders the first 256 rows of whichever split you pick.