The /3 subnet
A /3 subnet uses the mask 224.0.0.0 and holds 536,870,912 addresses, 536,870,910 of them usable.
A /3 is a very large IPv4 block. Its mask is 224.0.0.0 and it holds 536,870,912 addresses, which puts it at the scale of a regional allocation or an entire private supernet rather than a single LAN.
Networks this size are almost always carved into smaller subnets before use. You will see a /3 as an aggregate route or a private-address supernet such as 10.0.0.0/8, not as a single broadcast domain.
Below you can see the exact network, broadcast, and host range for any /3 you enter, calculated instantly in your browser.
Calculate a /3 network
Accepts CIDR (192.0.2.0/24), IP + mask (192.0.2.0 255.255.255.0), or a bare IP (defaults to /24).
00001010.00000000.00000000.0000000011100000.00000000.00000000.00000000Example: 10.0.0.0/3
Taking 10.0.0.0/3 as a worked example, the block breaks down like this:
| Network address | 0.0.0.0 |
|---|---|
| Usable range | 0.0.0.1 - 31.255.255.254 |
| Broadcast address | 31.255.255.255 |
| Total addresses | 536,870,912 |
| Usable hosts | 536,870,910 |
| Size | 32 class A blocks |
Frequently asked questions
What is the subnet mask for a /3?
A /3 uses the subnet mask 224.0.0.0. Its wildcard mask, used in access lists, is 31.255.255.255.
How many hosts are in a /3 subnet?
A /3 has 536,870,912 total addresses and 536,870,910 usable hosts (the total minus the network and broadcast addresses, except for /31 and /32).
What is a /3 used for?
Very large network. It is equivalent to 32 class A blocks.
How do I calculate a /3 network?
Set the host bits to zero for the network address and to one for the broadcast address. The calculator on this page does it for any /3 block you enter.