Subnet Calculator (CIDR)
Enter an IP address and CIDR prefix — get the network and broadcast address, masks, host range and count. Entirely in your browser.
The most looked-up mask is /24: 255.255.255.0 — 256 addresses, 254 usable hosts. The full /0–/32 table is below.
All CIDR prefixes
| CIDR | Mask | Addresses | Usable hosts |
|---|---|---|---|
| /0 | 0.0.0.0 | 4,294,967,296 | 4,294,967,294 |
| /1 | 128.0.0.0 | 2,147,483,648 | 2,147,483,646 |
| /2 | 192.0.0.0 | 1,073,741,824 | 1,073,741,822 |
| /3 | 224.0.0.0 | 536,870,912 | 536,870,910 |
| /4 | 240.0.0.0 | 268,435,456 | 268,435,454 |
| /5 | 248.0.0.0 | 134,217,728 | 134,217,726 |
| /6 | 252.0.0.0 | 67,108,864 | 67,108,862 |
| /7 | 254.0.0.0 | 33,554,432 | 33,554,430 |
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /9 | 255.128.0.0 | 8,388,608 | 8,388,606 |
| /10 | 255.192.0.0 | 4,194,304 | 4,194,302 |
| /11 | 255.224.0.0 | 2,097,152 | 2,097,150 |
| /12 | 255.240.0.0 | 1,048,576 | 1,048,574 |
| /13 | 255.248.0.0 | 524,288 | 524,286 |
| /14 | 255.252.0.0 | 262,144 | 262,142 |
| /15 | 255.254.0.0 | 131,072 | 131,070 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /17 | 255.255.128.0 | 32,768 | 32,766 |
| /18 | 255.255.192.0 | 16,384 | 16,382 |
| /19 | 255.255.224.0 | 8,192 | 8,190 |
| /20 | 255.255.240.0 | 4,096 | 4,094 |
| /21 | 255.255.248.0 | 2,048 | 2,046 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /23 | 255.255.254.0 | 512 | 510 |
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 |
| /32 | 255.255.255.255 | 1 | 1 |
Frequently asked questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) writes a network as address + prefix length: 192.168.1.0/24 means the first 24 bits are the network part. It replaced the old classful system (A/B/C) and allows arbitrarily sized blocks.
How is the network address calculated?
By a bitwise AND between the IP address and the subnet mask. For example 192.168.1.10 AND 255.255.255.0 = 192.168.1.0 — the network address of the /24 block.
Why are there 2 fewer hosts than addresses?
The first address in a block is the network address and the last is the broadcast address; neither is assigned to a device. Exceptions: /31 (RFC 3021, both addresses used on point-to-point links) and /32 (a single host).
What is a wildcard mask?
The inverse of the subnet mask (bitwise NOT). It is used in Cisco ACLs and OSPF configuration: for /24 the mask is 255.255.255.0 and the wildcard is 0.0.0.255.
Which IP ranges are private?
Per RFC 1918: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. They are not routed on the internet and are used in home and corporate networks behind NAT.