1 · IP address
2 · Prefix / mask
3 · Split into subnets
Divides this block into 4 × /26 subnets. Need different sizes? Use the VLSM calculator →
The prefix decides everything
An IPv4 address is 32 bits. The prefix (the /n) splits those bits into a network part and a host part. Everything else — how many hosts you get, the broadcast address, the mask — falls out of where that boundary sits. Our bit-grid colours the split so you can see it.
Need different-sized subnets from one block? Use the VLSM calculator. Want the quick reference? The subnet cheat sheet lists every prefix.
Subnetting — common questions
What does a subnet calculator do?
It takes an IP address and a prefix length (or subnet mask) and works out the network address, broadcast address, the first and last usable host, the number of usable and total addresses, the subnet mask and wildcard mask, the legacy class, and whether the address is public, private or special-use. Ours does it live as you type, shows the result in binary, detects the address scope, and can split the block into smaller subnets.
What does /24 (or a prefix like /26) mean?
The number after the slash is the prefix length — how many of the 32 bits identify the network. A /24 fixes the first 24 bits (mask 255.255.255.0), leaving 8 bits for hosts → 256 addresses, 254 usable. Each extra bit halves the hosts: /25 = 126 usable, /26 = 62, /27 = 30, /28 = 14, /29 = 6, /30 = 2. Our bit-grid shows exactly where the network/host boundary falls.
How many usable hosts are in a subnet?
For a normal subnet it is 2^(32−prefix) − 2 (you subtract the network and broadcast addresses). So /24 = 254, /26 = 62, /30 = 2. Two special cases: a /31 has 2 usable addresses for point-to-point links (RFC 3021), and a /32 is a single-host route. Many calculators get /31 wrong — ours follows the RFC.
Is this address public or private?
The calculator flags the scope automatically. Private ranges (RFC 1918) are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16; carrier-grade NAT is 100.64.0.0/10 (RFC 6598); 169.254.x.x is link-local (RFC 3927); 127.x.x.x is loopback; 192.0.2/198.51.100/203.0.113 are documentation ranges (RFC 5737). Anything else routable is public (global unicast).
What is the wildcard mask?
The wildcard mask is the bitwise inverse of the subnet mask (e.g. /24 → mask 255.255.255.0, wildcard 0.0.0.255). It is used in access control lists (ACLs) and OSPF on Cisco and other routers to match a range of addresses. The calculator shows it alongside the subnet mask.
Does Servnet design networks?
Yes — as a 24-year UK IT partner we design, supply and support enterprise networks built on Cisco, HPE Aruba, Juniper and Fortinet, from IP addressing and segmentation to switching, routing, Wi-Fi and SD-WAN. This free tool is the planning piece; talk to us for the build.