How it works
An IPv4 address is four decimal octets from 0 to 255. The prefix identifies the leading network bits; a valid subnet mask contains contiguous 1 bits followed by 0 bits. The entered address may be anywhere in the block: its host offset is the zero-based distance from the network address. Prefixes /0 through /30 use traditional first/last address reservation. A /31 uses the point-to-point convention with two endpoints and no directed broadcast; a /32 is a single host route. Counts describe mathematical capacity, not authorization, assignment, reachability or usable public Internet space. Special-purpose and reserved address ranges are not filtered out.
The formulaAddresses = 2^(32 - prefix length)
Network = floor(address integer / addresses) x addresses
Last address = network + addresses - 1
Traditional usable count = addresses - 2
/31 point-to-point: 2 endpoints; /32 host route: 1 address
Split count = 2^(target prefix - parent prefix)
Put it into practice
EXAMPLE192.168.1.130 with /24 or 255.255.255.0 belongs to 192.168.1.0/24. It contains 256 addresses, with a traditional usable range of 192.168.1.1–192.168.1.254. The entered address has host offset 130.
EXAMPLESplit 192.168.1.0/24 into /26 blocks to get four equal subnets of 64 addresses each. Requesting three subnets rounds up to four and partitions the entire parent.
EXAMPLE192.0.2.10/31 has two point-to-point endpoints: 192.0.2.10 and 192.0.2.11. 192.0.2.10/32 is a single-address host route.
Good to know
Can I paste an address with /24?
Yes. Use an address such as 192.168.1.130/24. The separate prefix/netmask field must match, or be blank. Leading zeros, shortened addresses, hexadecimal and noncontiguous masks are rejected.
What does requesting a subnet count mean?
The count rounds up to the next power of two. All subnets have equal size and together cover the entire normalized parent network. One subnet means the parent itself. This is not a variable-length allocation planner.
How big can the split list be?
Even /0 split into /32 is calculated immediately: only 40 rows are rendered per page. Jump directly to any page. Export the current page, or export the entire plan when it has at most 4,096 subnets. Larger plans are never silently truncated.
Are /31 and /32 always assignable to devices?
No. /31 assumes a supported point-to-point link. /32 describes a host route. Equipment, provider and address-allocation rules still apply. A displayed count does not make multicast, reserved or other special-purpose space assignable.
Does it inspect my network or support IPv6?
No. This IPv4-only calculator runs locally. It does not scan hosts, query IP ownership, geolocate addresses, send inputs to a server or change network settings.