IP Subnet Calculator

A /24 subnet uses a 255.255.255.0 mask and contains 256 IP addresses, of which 254 are usable for hosts. The /24 means the first 24 bits are the network portion, leaving 8 bits for hosts, and two addresses are reserved (the network address and the broadcast address). Nearby sizes scale by powers of two:

• /23 doubles the block to 512 addresses
• /24 holds 256 addresses
• /25 halves it to 128 addresses

A /24 is a common size for a home or small office LAN, such as 192.168.1.0/24. The calculator above shows the exact network, broadcast, and host range for any address and prefix you enter.

The usable host count is 2 to the power of the host bits, minus 2 for IPv4. Host bits equal 32 minus the prefix length, so a /26 leaves 6 host bits, giving 2^6 = 64 total addresses and 62 usable. The two subtracted addresses are the network address, which names the subnet, and the broadcast address, which reaches every host at once. Two prefixes are exceptions:

• /31 provides 2 addresses for point-to-point links, with no broadcast
• /32 describes a single host

IPv6 keeps the same 2^(host bits) math but does not reserve a network or broadcast address, so every address in the prefix can be assigned.

Private IP ranges are blocks reserved for internal networks that are not routed on the public internet. RFC 1918 defines three for IPv4:

• 10.0.0.0/8 for large networks
• 172.16.0.0/12 for medium networks
• 192.168.0.0/16 for home and small office routers

Devices on these ranges reach the internet through NAT, which translates the private address into a public one. IPv6 has an equivalent called unique local addresses in the fd00::/8 range. Paste any private range into the calculator above to see how many addresses it holds and how to divide it into smaller subnets.

A /16 contains 256 subnets of size /24, because the prefix grows by 8 bits and 2^8 is 256. Each extra prefix bit doubles the number of subnets and halves their size:

• a /16 splits into 2 /17s
• then 4 /18s
• and so on, up to 256 /24s

The general rule is 2 raised to the difference between the two prefix lengths. A /16 holds 65,536 addresses in total, and each /24 inside it holds 256. To see every block at once, enter a network above and use the split option by new prefix length, then export the list to CSV.

A subnet mask marks the network bits with ones, and a wildcard mask is its exact inverse, marking the host bits with ones. For a /24:

• subnet mask: 255.255.255.0
• wildcard mask: 0.0.0.255

You use the subnet mask to configure an interface or define a network, and the wildcard mask when you write access control lists or OSPF statements that match a range. For example, an ACL line referencing 192.168.1.0 0.0.0.255 matches the whole /24. The calculator above shows both masks for any prefix so you can copy the exact value your configuration expects.

IPv6 subnetting follows the same prefix logic as IPv4 but differs in three practical ways:

• No broadcast address: nothing is reserved and every address can be assigned; IPv6 uses multicast instead
• /64 is the standard size for a single network, far larger than any IPv4 subnet
• Hexadecimal notation with colons rather than dotted decimal

The calculator above reflects this by showing the first and last address of an IPv6 prefix instead of network and broadcast labels. Because IPv6 ranges can be enormous, very large splits are capped in the results table for performance, while the address math stays exact.

Splitting a network means borrowing host bits to create several smaller subnets from one larger block. Borrow 2 bits from a /24 and you get four /26 subnets of 62 usable hosts each. VLSM (variable length subnet masking) lets you mix sizes, giving a busy segment a /25 and a small one a /28 from the same parent. The calculator above can divide a network three ways:

• by a target number of subnets
• by the hosts each subnet must hold
• by a new prefix length

It then lists each block with its host range so you can assign them directly.

Yes. The calculator is free and runs entirely in your browser, so no address you enter is sent to a server and nothing is stored. The math happens locally on your device, and you can share a result by copying the page link, which encodes your inputs in the URL. The tool needs no account or sign-up. Once your addressing is planned and the hosts are live, you can watch the services running on them with WebPixie uptime monitoring, and review the free plan and paid tiers on the pricing page.