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CIDR to Subnet Mask Converter
Convert CIDR prefix length (e.g. /24) to a dotted-decimal subnet mask. Includes a full reference table of all CIDR notations.
CIDR Prefix
/
Subnet Mask
255.255.255.0
/24 — 254 usable hosts
CIDR Reference Table
| CIDR | Subnet Mask | Usable Hosts |
|---|---|---|
| /0 | 0.0.0.0 | 4,294,967,296 |
| /1 | 128.0.0.0 | 2,147,483,648 |
| /2 | 192.0.0.0 | 1,073,741,822 |
| /3 | 224.0.0.0 | 536,870,910 |
| /4 | 240.0.0.0 | 268,435,454 |
| /5 | 248.0.0.0 | 134,217,726 |
| /6 | 252.0.0.0 | 67,108,862 |
| /7 | 254.0.0.0 | 33,554,430 |
| /8 | 255.0.0.0 | 16,777,214 |
| /9 | 255.128.0.0 | 8,388,606 |
| /10 | 255.192.0.0 | 4,194,302 |
| /11 | 255.224.0.0 | 2,097,150 |
| /12 | 255.240.0.0 | 1,048,574 |
| /13 | 255.248.0.0 | 524,286 |
| /14 | 255.252.0.0 | 262,142 |
| /15 | 255.254.0.0 | 131,070 |
| /16 | 255.255.0.0 | 65,534 |
| /17 | 255.255.128.0 | 32,766 |
| /18 | 255.255.192.0 | 16,382 |
| /19 | 255.255.224.0 | 8,190 |
| /20 | 255.255.240.0 | 4,094 |
| /21 | 255.255.248.0 | 2,046 |
| /22 | 255.255.252.0 | 1,022 |
| /23 | 255.255.254.0 | 510 |
| /24 | 255.255.255.0 | 254 |
| /25 | 255.255.255.128 | 126 |
| /26 | 255.255.255.192 | 62 |
| /27 | 255.255.255.224 | 30 |
| /28 | 255.255.255.240 | 14 |
| /29 | 255.255.255.248 | 6 |
| /30 | 255.255.255.252 | 2 |
| /31 | 255.255.255.254 | 1 |
| /32 | 255.255.255.255 | 1 |
What is CIDR Notation?
CIDR (Classless Inter-Domain Routing) notation is a compact way to specify an IP address and its
associated subnet mask. It appends a slash and a number to an IP address — for example,
192.168.1.0/24. The number after the slash is the prefix length,
indicating how many of the 32 bits in the address are the network part.
How Conversion Works
The CIDR prefix length tells you how many leading bits of the subnet mask are set to 1.
A /24 means the first 24 bits are 1 and the remaining 8 bits are 0, giving a mask of
11111111.11111111.11111111.00000000 = 255.255.255.0.
Common CIDR Prefixes
- /8 — 255.0.0.0 — Class A default (16M addresses)
- /16 — 255.255.0.0 — Class B default (65K addresses)
- /24 — 255.255.255.0 — Class C default (256 addresses)
- /30 — 255.255.255.252 — Point-to-point links (4 addresses)
- /32 — 255.255.255.255 — Single host (1 address)