Time Converter

Convert between every common unit of time.

📖 Read the full guide: Time Units: Why a Year Isn't Exactly 365 Days In-depth article explaining the math and real-world context. →

Time Unit Quick References

Unit	Seconds
1 millisecond	0.001 s
1 minute	60 s
1 hour	3,600 s
1 day	86,400 s
1 week	604,800 s
1 month (average)	2,629,800 s (30.4375 days)
1 Julian year (365.25 d)	31,557,600 s
1 Gregorian year (365.2425 d)	31,556,952 s
1 sidereal year	31,558,150 s (Earth's orbit, astronomical)

Why Months and Years Are Approximate

"Months" and "years" don't have a single exact value:

Months vary from 28 days (February) to 31 days. Average = 30.4375 days/month.
Julian year = 365.25 days. Used widely in astronomy for clean math.
Gregorian year = 365.2425 days. The civil calendar year (with leap year rules).
Tropical year = 365.2422 days. The Earth's actual orbital period around the Sun.

This calculator uses 30.4375-day months and 365.25-day years for those conversions. The Wikipedia article on year definitions details all the variations.

Notable Time Facts

1 day ≠ exactly 86,400 seconds — Earth's rotation slows ~1.7 ms/century, so leap seconds are inserted occasionally
1 light-year is a distance unit (~9.46 trillion km), not a time unit, despite the name
Coordinated Universal Time (UTC) — international time standard since 1972, defined by atomic clocks
Unix time — seconds since Jan 1, 1970 UTC. Will overflow 32-bit signed integers in January 2038 (the "Y2K38" bug)