Free IPv4 Subnet Calculator

Type any valid IPv4 address into the IP Address field. The calculator accepts any address in dotted-decimal notation — four octets, each between 0 and 255.

1. 1Click the IP Address field at the top left.
2. 2Type your address, e.g. 192.168.0.1, 10.0.0.50, or 172.16.5.100.
3. 3The Subnet Details table refreshes automatically — no button press needed.

You have two ways to define the subnet size — both controls stay in sync automatically.

1. ASubnet Mask field: Type a standard dotted-decimal mask such as 255.255.255.0 or 255.255.0.0. The CIDR slider jumps to match instantly.
2. BCIDR Slider: Drag left or right — from /0 (entire internet block) to /32 (single host). The subnet mask field updates in real time.

Every row in the results table explained:

1. →Network Address — First address of the block; identifies the network and cannot be assigned to a host.
2. →First / Last Usable IP — The assignable host range: network + 1 through broadcast − 1.
3. →Broadcast Address — Last address of the subnet; packets sent here reach all hosts simultaneously.
4. →Total Usable Hosts — Assignable addresses = 2^{(32−prefix)} − 2. Special cases: /31 = 2 (RFC 3021 P2P), /32 = 1 (host route).
5. →Total Available Hosts — Full block size = 2^{(32−prefix)}. Includes the network address and broadcast address. For a /24 this is 256; for a /26 this is 64.
6. →Wildcard Mask — Bitwise inverse of the subnet mask; used in router ACLs and OSPF area statements.
7. →Binary Subnet Mask — 32-bit binary view split into octets, making the network/host boundary clearly visible.

Example — IP 10.0.0.50 with prefix /26

This tool handles single-subnet inspection. For multi-subnet planning, use the specialized tools in the navigation menu above:

1. →FLSM Calculator — Divide a network into equal-sized subnets with Fixed-Length Subnet Masking.
2. →VLSM Calculator — Allocate subnets of varying sizes based on per-segment host requirements, minimising wasted addresses.
3. →Supernetting / Route Summarization — Combine multiple contiguous networks into one optimal summary route.
4. →IPv6 Calculator — Plan and inspect IPv6 subnets and prefixes.

A subnet mask is a 32-bit number that divides an IP address into a network portion and a host portion. Bits set to 1 identify the network; bits set to 0 identify the specific host within that network. For example, 255.255.255.0 (/24) means the first 24 bits are the network and the last 8 bits identify hosts — allowing up to 254 usable addresses.

CIDR (Classless Inter-Domain Routing) notation expresses a network as an IP address followed by a slash and the count of leading 1-bits in the subnet mask — e.g. 192.168.1.0/24. It replaced the rigid Class A/B/C system and allows flexible, efficient address allocation. The number after the slash is called the prefix length and ranges from /0 to /32.

Total Usable Hosts is the count of addresses you can actually assign to devices — calculated as 2^{(32−prefix)} − 2, subtracting the network address and broadcast address. Total Available Hosts is the full block size — 2^{(32−prefix)} — counting all addresses including those two reserved ones. For a /24: usable = 254, available = 256. For a /26: usable = 62, available = 64.

A wildcard mask is the bitwise inverse of the subnet mask. A 0 bit means "this bit must match" and a 1 bit means "any value is accepted." Wildcard masks are used in Cisco router ACLs (access control lists) and in OSPF network statements to define which addresses a rule applies to. For a /24 network the wildcard mask is 0.0.0.255.

Use the formula: 2^{(32 − prefix length)} − 2. Subtract 2 to exclude the network address and broadcast address, neither of which can be assigned to a device. For example, a /24 gives 2⁸ − 2 = 254 usable hosts; a /26 gives 2⁶ − 2 = 62 usable hosts. Special cases: /31 = 2 hosts (RFC 3021 point-to-point link), /32 = 1 host (host route).

A /31 subnet (defined in RFC 3021) provides exactly 2 addresses for point-to-point links — no separate network or broadcast address is needed, so both addresses are usable. A /32 is a host route representing one specific IP address, commonly used on loopback interfaces and in BGP next-hop configurations. This calculator handles both correctly.

This Subnet Calculator is designed for inspecting a single network block — it instantly shows you the network address, usable host range, broadcast address, wildcard mask, and binary representation for one IP and mask combination. The FLSM Calculator divides a network into multiple equal-sized subnets, while the VLSM Calculator allocates subnets of varying sizes based on individual host requirements for each segment.