Convert an IPv4 prefix length into a dotted netmask and back.
Type or paste on the left — the result updates as you type.
Accepts prefixes 0–32. Reverse conversion rejects masks whose binary ones are not contiguous.
Up to 100,000 UTF-16 units per input and 1,000,000 per result. See the supported formats and examples below.
Tool page updated: 2026-09-27
