IP Subnet Calculator
Type an IP address with a prefix or subnet mask to get the network and broadcast address, usable host range, wildcard mask and binary view — then split it into subnets, plan VLSM or summarise routes.
At a glance
- Works out the network address, broadcast address, first and last usable host, total and usable addresses, subnet mask, wildcard mask and binary form of any IPv4 or IPv6 block.
- Accepts CIDR (192.168.1.10/24), an address with a mask (10.0.0.1 255.255.240.0), a Cisco wildcard mask, or IPv6 in any notation, and writes IPv6 the RFC 5952 way.
- Names the address type — private (RFC 1918), CGNAT (100.64.0.0/10), loopback, link-local, multicast, documentation, unique local or global unicast — and the classful class.
- Splits a network into equal subnets by count, hosts or prefix, plans VLSM (largest subnet first) and summarises lists of networks or ranges into the fewest CIDR blocks.
- Handles the edge cases exams ask about: /31 point-to-point links (RFC 3021), /32 hosts, /0, and IPv6 counts too big for ordinary numbers.
- Gives the reverse DNS zone (in-addr.arpa / ip6.arpa), checks whether an address is inside the network, and exports subnet tables as CSV. Everything is calculated in your browser.
Step by step
How to calculate a subnet
- 1
Enter an address
Type an IP with its prefix, such as 192.168.1.10/24, or pick the subnet mask from the list.
- 2
Read the results
See the network address, broadcast address, usable host range and number of hosts instantly.
- 3
Split or plan
Switch to Split network to divide it into subnets, or VLSM to size subnets for each LAN.
- 4
Export
Copy the details or download the subnet table as CSV for your documentation.
Features
Everything you need, nothing you don’t
Every subnet value
Network, broadcast, host range, mask, wildcard, hex, binary and reverse DNS — copy them all in one click.
IPv4 and IPv6
One calculator for both, with BigInt maths so even a /32 IPv6 allocation is counted exactly.
Subnetting made easy
Split a network by the number of subnets or hosts you need, and see every resulting subnet in a table.
VLSM planner
List your LANs and how many devices each has; get the smallest fitting subnet for each, with room to grow shown.
Route summarisation
Merge networks, single addresses and ranges into the fewest CIDR blocks, or find the one supernet that covers them.
Exam-ready
Binary view with network bits highlighted, class and the /31 and /32 rules — handy for CCNA and university networking.
IPv4 subnet mask cheat sheet
| Prefix | Subnet mask | Wildcard | Addresses | Usable hosts |
|---|---|---|---|---|
| /8 | 255.0.0.0 | 0.255.255.255 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 0.0.255.255 | 65,536 | 65,534 |
| /20 | 255.255.240.0 | 0.0.15.255 | 4,096 | 4,094 |
| /21 | 255.255.248.0 | 0.0.7.255 | 2,048 | 2,046 |
| /22 | 255.255.252.0 | 0.0.3.255 | 1,024 | 1,022 |
| /23 | 255.255.254.0 | 0.0.1.255 | 512 | 510 |
| /24 | 255.255.255.0 | 0.0.0.255 | 256 | 254 |
| /25 | 255.255.255.128 | 0.0.0.127 | 128 | 126 |
| /26 | 255.255.255.192 | 0.0.0.63 | 64 | 62 |
| /27 | 255.255.255.224 | 0.0.0.31 | 32 | 30 |
| /28 | 255.255.255.240 | 0.0.0.15 | 16 | 14 |
| /29 | 255.255.255.248 | 0.0.0.7 | 8 | 6 |
| /30 | 255.255.255.252 | 0.0.0.3 | 4 | 2 |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 | 2 (point-to-point) |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | 1 (single host) |
Private and special IPv4 ranges
| Range | Use |
|---|---|
| 10.0.0.0/8 | Private network (RFC 1918) — large companies and data centres |
| 172.16.0.0/12 | Private network (RFC 1918) — 172.16.0.0 to 172.31.255.255 |
| 192.168.0.0/16 | Private network (RFC 1918) — home and office routers |
| 100.64.0.0/10 | Carrier-grade NAT — ISPs, especially mobile data, share public IPs |
| 169.254.0.0/16 | Link-local — self-assigned when DHCP fails |
| 127.0.0.0/8 | Loopback — the computer itself (localhost) |
How subnetting works
An IPv4 address has 32 bits. The prefix length — the number after the slash — says how many of them identify the network; the rest number the hosts inside it. A /24 leaves 8 host bits, so 2⁸ = 256 addresses. The first is the network address and the last the broadcast address, so 254 are usable for devices.
Every extra prefix bit halves the block: a /24 splits into two /25s, four /26s or eight /27s. VLSM (variable-length subnet masking) uses different sizes inside one network — a /25 for 100 office PCs, a /30 for a router link — to avoid wasting addresses. IPv6 LANs simply use /64 each; sites usually get a /48 or /56.
FAQ
Frequently asked questions
How many usable hosts does a /24 have?
What is a wildcard mask?
How do I find the network and broadcast address?
Can a /31 be used?
What subnet size should I use for an IPv6 LAN?
What is VLSM?
Keep going
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