IPv4 Subnet Calculator
Inspect IPv4 networks and plan aligned, nonoverlapping subnets for different host requirements. See exact address counts, /31 links, /32 routes and remaining CIDR blocks.
Inspect an IPv4 network, or fit networks with different host requirements into one parent block.
Networks to fit
LANs reserve network and broadcast addresses. /31 links require RFC 3021 support at both ends. Names are optional.
Network containing your address
192.168.10.0/24
Address block: 192.168.10.0 – 192.168.10.255
- Total addresses
- 256
- LAN host slots
- 254
- Subnet mask
- 255.255.255.0
- Wildcard mask
- 0.0.0.255
Host range: 192.168.10.1 – 192.168.10.254
Directed broadcast: 192.168.10.255
LAN convention: two addresses are reserved. Special-purpose ranges and provider reservations may reduce availability.
Largest networks first · aligned blocks
- Allocated addresses
- Unallocated addresses
- Requested hosts / endpoints
- Spare slots inside allocations
Each colored block occupies its exact share of the parent. Select a network below to inspect even the smallest block.
The allocation table scrolls horizontally on small screens.
| Network | CIDR | Host / endpoint range | Requested | Slots | Spare |
|---|
Unallocated address blocks
These are addresses, not a single pool of usable LAN hosts. Each new LAN needs its own network and broadcast addresses.
/31 allocations are point-to-point links only; /32 allocations are single-address routes. This is an address plan, not a claim that every address is routable or assignable.
The entered IPv4 address stays the same. Changing the prefix changes the containing network.
24 network bits · 8 host bits
How the subnet plan works
The prefix counts network bits in a 32-bit IPv4 address. A /24 leaves 8 host bits: 2⁸ = 256 addresses. For a conventional LAN, subtract the network and directed broadcast addresses to get 254 host slots.
VLSM assigns the smallest power-of-two block that fits each requirement. It places larger blocks first, preserving your order for equal sizes, and aligns each block within the parent. If all requirements cannot fit, no partial plan is presented.
Why /31 and /32 are different
RFC 3021 permits both addresses of a /31 on a point-to-point link. It does not make a /31 a general-purpose LAN; both ends must support this convention. There is no directed broadcast. A /32 identifies one address, commonly used as a host route, with no directed broadcast.
Input and scope
Use four decimal octets from 0 to 255, without leading zeroes, and a prefix from /0 to /32 or a contiguous dotted subnet mask. This tool supports IPv4 only. Host requirements are positive whole numbers; properly grouped English commas are accepted. LANs use at least /30, /31 links require exactly two endpoints, and /32 routes require exactly one address. Up to 64 networks can be planned.
Counts describe address conventions. Private, documentation, multicast, unspecified, loopback, broadcast and other special-purpose addresses are not all globally assignable. CSV exports prefix formula-like names with “Text: ” to keep them as text. Cloud providers may reserve additional addresses. Check your environment before applying the plan. The calculator does not configure or scan a network.
Standards: RFC 4632: CIDR, RFC 3021: /31 point-to-point links, RFC 1878: IPv4 mask table.
