3 Free Online Number Tools
Three conversions come up constantly in development work, and all 3 are here. Number Base Converter moves an integer between binary, octal, decimal, and hexadecimal — the arithmetic behind a permission bitmask, a colour value, or a memory address — and handles numbers far beyond 64 bits using BigInt. UNIX Timestamp Converter turns epoch seconds or milliseconds into a readable local, UTC, and ISO 8601 date, and converts back the other way, which is what you need the moment a log line or a database column gives you 1735689600 and no context. UUID Generator produces version 4 identifiers in bulk from the browser cryptographic random source, for seeding test data or filling an ID column by hand.
All 3 Number tools
What you can do with these number tools
Small conversions, but the kind that are easy to get subtly wrong in your head or in a throwaway script.
- Convert bases — binary, octal, decimal, and hexadecimal in any direction, including very large values via BigInt.
- Read timestamps — convert epoch seconds or milliseconds to local time, UTC, and ISO 8601, and turn a date back into a timestamp.
- Generate identifiers — create one or up to 100 UUID v4 values at a time, ready to paste into fixtures or a database.
Seconds or milliseconds, and other easy mistakes
The classic timestamp bug is a unit mismatch: UNIX time is seconds, but JavaScript Date.now() and most JVM APIs return milliseconds, so a value pasted from the wrong side lands in 1970 or in the year 56000. A ten-digit number is almost certainly seconds and a thirteen-digit one milliseconds — the converter detects this, but it is worth recognising yourself. The other recurring trap is timezones: an epoch value has no timezone at all, it is an absolute instant, and the local time you see depends entirely on the machine rendering it. When you compare a timestamp from a log against one from a database, compare the epoch values, not the formatted strings.