CIDR Calculator
Convert between CIDR notation and subnet masks, and see how many addresses each prefix length provides.
Your details
This calculator runs entirely on your device. Nothing you enter is uploaded, stored, or sold. How this works
/24
255.255.255.0
254 usable addresses out of 256 total
Includes your inputs, the full breakdown, and every row of the table.
Total addresses
256
Usable hosts
254
Wildcard mask
0.0.0.255
Legacy class
Class C
- CIDR prefix
- /24
- Subnet mask
- 255.255.255.0
- Wildcard mask
- 0.0.0.255
- Host bits
- 8
- Total addresses
- 256
- Usable hosts
- 254
- Equivalent /24 blocks
- 1
| CIDR | Subnet mask | Addresses | Usable hosts |
|---|---|---|---|
| /32 | 255.255.255.255 | 1 | 1 |
| /31 | 255.255.255.254 | 2 | 2 |
| /30 | 255.255.255.252 | 4 | 2 |
| /29 | 255.255.255.248 | 8 | 6 |
| /28 | 255.255.255.240 | 16 | 14 |
| /27 | 255.255.255.224 | 32 | 30 |
| /26 | 255.255.255.192 | 64 | 62 |
| /25 | 255.255.255.128 | 128 | 126 |
| /24 | 255.255.255.0 | 256 | 254 |
| /23 | 255.255.254.0 | 512 | 510 |
What this means
- Each step down in prefix length doubles the address space. A /23 is exactly two /24s.
- Cloud providers reserve extra addresses inside each subnet. AWS reserves five per subnet and Azure reserves five, so a /28 gives you 11 usable addresses, not 14.
How the cidr calculation works
CIDR replaced the old class-based addressing system with a flexible prefix length. Rather than being locked into Class A, B, or C boundaries, any prefix from /0 to /32 is valid, which lets networks be sized to actual need.
The arithmetic is all powers of two. A prefix of length P leaves 32−P host bits, giving 2^(32−P) addresses. Every reduction of the prefix by one doubles the block size, which is why /23 is two /24s and /22 is four.
Frequently asked questions
What does /24 mean?
The first 24 bits are the network portion, leaving 8 host bits — 256 addresses, 254 usable. It is equivalent to a 255.255.255.0 subnet mask.
What CIDR do I need for 1000 hosts?
A /22 gives 1022 usable addresses. A /23 only gives 510, so it would not be enough.
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Disclaimer. This calculator is provided for general information and educational purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Results are estimates based on the inputs you provide and the assumptions described above. Confirm any figure with a qualified professional before acting on it.