Subnet & CIDR Calculator: IP Ranges, Masks, Hosts

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 classification Private-use (192.168.0.0/16 · IANA Globally Reachable: No)

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 classification Private-use (10.0.0.0/8 · IANA Globally Reachable: No)

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. It also classifies the address against IANA’s special-purpose registry. 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).

How the address classification works

The calculator checks the IPv4 address you typed against every prefix in IANA’s special-purpose registry. When entries overlap, the longest prefix wins. That matters inside 192.0.0.0/24: 192.0.0.1 matches the non-global service-continuity /29, while the more-specific PCP address at 192.0.0.9/32 and TURN address at 192.0.0.10/32 have a Globally Reachable value of Yes. The dummy address at .8 and NAT64/DNS64 discovery addresses at .170 and .171 have a value of No.

The retired 192.88.99.0/24 6to4 relay entry has blank registry flags, so the calculator reports its global-reachability value as Unknown. Its more-specific 192.88.99.2/32 entry explicitly says No. This is why checking only a broad parent block can give the wrong answer.

Common results include:

The classification belongs to the input address alone. A /24 result can contain more-specific exceptions with different registry values. An address with no matching special-purpose prefix is labeled “No special-use restriction identified.” That does not certify address allocation, a working route, firewall permission, or end-to-end reachability.

Multicast 224.0.0.0/4 stays separate because IANA publishes it in the IPv4 multicast registry rather than the special-purpose registry. Home and homelab networks usually live in the RFC 1918 entries above. The equal-size split feature can carve a /24 into per-VLAN /26s or /27s, but it does not change the classification of the address you entered.

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 router guide covers the wireless layer, and the budget networking gear guide rounds up switches and routers worth buying.

Assumptions and sources

• The classifier snapshot covers all 25 rows in the IANA IPv4 Special-Purpose Address Registry, expanded to 26 prefixes because the NAT64/DNS64 row contains two /32 addresses. IANA last updated this registry on 2025-10-09; the CSV and XML used here were retrieved on 2026-10-23. Blank flags remain unknown rather than being converted to Yes or No.
• The classifier uses longest-prefix matching. It treats IANA’s Globally Reachable field as a registry classification, not a live network test. A Yes value or no matching special-purpose entry does not establish ownership, address allocation, BGP routing, firewall policy, host availability, or end-to-end reachability.
• The multicast range (224.0.0.0/4) is outside the special-purpose registry. IANA tracks it separately in the IPv4 Multicast Address Space Registry. RFC 1112 defines the Class D block, and RFC 5771 describes its assignment rules.
• The /31 exception - two usable addresses on point-to-point links, with no network/broadcast pair - is per RFC 3021.
• Network and broadcast addresses, host counts, masks, wildcard masks, and equal-size splits use 32-bit arithmetic. Address classification uses the entered IP, not the calculated network address or the whole resulting subnet.