Time Converter

The second is the SI base unit of time, defined by fixing the caesium-133 hyperfine transition frequency at exactly 9,192,631,770 Hz. Sub-second units follow SI prefixes: millisecond (ms = 10⁻³ s), microsecond (µs = 10⁻⁶ s), nanosecond (ns = 10⁻⁹ s). Above the second the calendar takes over with non-decimal units: 60 seconds per minute, 60 minutes per hour, 24 hours per day. A Gregorian calendar year averages 365.2425 days; a Julian year is exactly 365.25 days, used in astronomy.

All conversions in this category are computed relative to a single base unit (Second) using factors sourced from NIST Special Publication 811 and the BIPM SI Brochure. A shared reference unit keeps the conversion relationships consistent. Converting directly from the original measurement avoids the rounding differences that can accumulate when displayed intermediate results are entered again.

This calculator supports 12 units, including Second, Millisecond, Microsecond, Nanosecond, Minute. Choose the unit shown in your source measurement, then the unit needed for your result.

Units may have alternate spellings or abbreviations. You can search using these names too. Examples include Second (s, also written as seconds or sec), or Millisecond (ms, also written as milliseconds or msec), or Microsecond (us, also written as microseconds or μs).

All time conversions within the SI family are purely multiplicative: you multiply the source value by a fixed conversion factor derived from the ratio of the two unit definitions. Imperial-to-metric conversions use the exact defined equivalences (e.g., 1 inch = 25.4 mm exactly) rather than approximations.

When precision matters, avoid rounding intermediate calculations. The displayed factors and results are rounded for readability, usually to ten significant digits; very large or small values use scientific notation. Use the original measurement for each conversion and round the final answer to match the accuracy of that measurement.

Keep the unit alongside each time value when you copy or share it. Check that the source and target units match your task. If two units have similar names, read their definitions before selecting one.

For a second check, use the worked example and formula on the conversion page. Start from your original value rather than a rounded result from another calculator. If you need to report a specific number of decimal places, round once at the end.