Free Subnet Calculator
Enter any IPv4 address and a CIDR prefix and this calculator instantly shows the network address, broadcast address, usable host range, subnet mask and wildcard mask — the exact answers CCNA, Network+ and Security+ subnetting questions ask for. Use it to check your work while you study, then learn to do it by hand below.
| IP address | |
|---|---|
| Subnet mask | |
| Wildcard mask | |
| Network address | |
| Broadcast address | |
| First usable host | |
| Last usable host | |
| Total addresses | |
| Usable hosts | |
| IP class | |
| Address scope |
How to check your answer by hand
On the exam there is no calculator — so use this tool to verify the magic-number method: the magic number is 256 minus the mask value in the interesting octet, subnets are multiples of that number, the broadcast address is one less than the next subnet, and usable hosts are everything in between. Worked examples, VLSM and a self-check quiz are in our guide: How to Subnet IPv4 in Under a Minute.
Subnetting shows up on CCNA and Network+ — practice free
Subnetting questions are guaranteed marks on the CCNA 200-301 and Network+ N10-009 exams. Try the free 30-question samples and see where you stand.
Free CCNA SampleFree Network+ SampleSubnet calculator FAQ
What is a subnet calculator?
A subnet calculator takes an IPv4 address and a prefix length (CIDR) and instantly works out the subnet's network address, broadcast address, usable host range, total and usable addresses, and subnet mask — the same values you have to calculate by hand on CCNA, Network+ and Security+ exams.
How many usable hosts are in a /26 subnet?
A /26 has 64 total addresses and 62 usable hosts. The first address is the network address and the last is the broadcast address, so usable hosts = 2^(32 − prefix) − 2 = 2^6 − 2 = 62.
What is the difference between the network address and the broadcast address?
The network address is the first address of a subnet and identifies the subnet itself; it cannot be assigned to a host. The broadcast address is the last address of the subnet and is used to reach every host in that subnet; it cannot be assigned to a host either. Usable hosts are all the addresses in between.
Is a /31 subnet usable?
Yes — on point-to-point links. RFC 3021 allows both addresses of a /31 to be used as endpoints, so a /31 gives 2 usable addresses with no network or broadcast address wasted. A /32 is a single host route with exactly 1 usable address.