How to use the cidr table lookup
- Look up any CIDR prefix from /0 to /32 to see its subnet mask, usable hosts, and block size.
- Click any row to copy the mask or wildcard to your clipboard.
- Bookmark for quick reference during ACL or VLAN planning.
CIDR Table Lookup
Masks and host counts
CIDR Table Lookup
Matching Prefix—
Subnet Mask—
Wildcard Mask—
Total IPs—
Usable Hosts—
Full CIDR Table
| CIDR | Subnet Mask | Wildcard | Total IPs | Usable Hosts |
|---|
Frequently asked questions
What is the subnet mask for /24?
/24 maps to 255.255.255.0 — eight host bits, 254 usable hosts per subnet. The classic 'Class C' size.
How many hosts fit in a /23?
A /23 has 9 host bits = 512 addresses, 510 usable. Two contiguous /24s aggregated into one larger subnet.
Why is /31 special in modern networks?
/31 follows RFC 3021: both of its 2 addresses are usable, saving two addresses on every point-to-point link.
What is the wildcard mask for /25?
/25 = 255.255.255.128. Its wildcard is the inverse: 0.0.0.127.