Runs locally in your browser. Nothing you enter is uploaded to our servers.
Accepts 255.255.255.0, /24, or 24.
Result will appear here
Tips for mask ↔ CIDR
Only contiguous masks are valid (e.g. 255.255.255.0, not 255.0.255.0).
/31 and /32 are valid for point-to-point and single-host cases.
Wildcard masks are inverted netmasks used in some ACLs.
Pair this with the CIDR calculator for network/broadcast ranges.
IPv6 prefixes are not converted here.
Mask, prefix, wildcard — same IPv4 idea
Processing stays in your browser — your input is not uploaded to our servers.
Dotted masks (255.255.255.0) and prefix lengths (/24) describe the same boundary. This converter switches between them and the wildcard mask ACLs like.
Invalid masks (holes in the bits) are rejected instead of quietly rounding.
Convert a subnet mask
Enter a mask or a prefix length
255.255.255.0 and 24 should round-trip to each other.
Read the other representations
Wildcard is the inverse bits — useful for some firewall syntaxes.
Paste into the device config
Do not mix prefix-length syntax on a CLI that only wants dotted masks.
Subnet mask FAQ
Is 255.255.0.255 valid?
No. Mask bits must be contiguous ones then zeros. This converter will not invent a prefix for a broken mask.
Does this assign addresses?
No. It only converts representations. Use the CIDR calculator for host counts.
Local only?
Yes. No network calls.