Time Converter

Convert between milliseconds, seconds, minutes, hours, days, weeks, months, and years instantly.

From

Quick Reference

How to Convert Time Units

Time conversion works by converting the input to the base unit (seconds), then to the target unit. This converter uses astronomical averages: 1 year = 365.25 days and 1 month = 30.4375 days (365.25/12) for the most accurate results.

Common Conversion Factors

From	To	Factor
Minute	Seconds	60
Hour	Seconds	3,600
Day	Seconds	86,400
Week	Seconds	604,800
Month (avg)	Seconds	2,629,800
Year (avg)	Seconds	31,557,600
Hour	Minutes	60

A Brief History of Time Measurement

Ancient civilizations used sundials and water clocks. The Babylonians divided the day into 24 hours and each hour into 60 minutes using their base-60 system. Mechanical clocks appeared in medieval Europe, and atomic clocks (1955) now define the second as 9,192,631,770 oscillations of a caesium-133 atom.

Common Durations

Duration	Seconds	Minutes	Hours
1 minute	60	1	0.0167
1 hour	3,600	60	1
1 day	86,400	1,440	24
1 week	604,800	10,080	168
1 month (avg)	2,629,800	43,830	730.5
1 year (avg)	31,557,600	525,960	8,766

Leap Years

A leap year has 366 days instead of 365, adding February 29th. The rule: divisible by 4, except centuries unless divisible by 400. So 2024 and 2028 are leap years, 1900 was not, but 2000 was. This keeps our calendar aligned with Earth's orbital period of ≈ 365.2422 days.

Time is the most consistent unit — until it is not

Seconds, minutes, hours, days, and weeks are universal and rigidly defined: the SI second is the duration of 9,192,631,770 periods of the radiation corresponding to a specific transition of the caesium-133 atom. Everything else (minutes = 60 s, hours = 3,600 s, days = 86,400 s for most purposes) follows arithmetically. Conversions become interesting at the edges: leap seconds, sidereal vs solar days, Julian vs Gregorian years, and the difference between a calendar month and a "month" in a finance formula.

Common conversions

Unit	Equals
1 minute	60 seconds
1 hour	60 minutes = 3,600 seconds
1 day	24 hours = 86,400 seconds
1 week	7 days = 604,800 seconds
1 fortnight	14 days
1 month (avg, Gregorian)	30.437 days = 730.5 hours
1 year (Gregorian)	365.2425 days = 8,765.82 hours
1 Julian year	365.25 days (used in astronomy)
1 sidereal day	23 h 56 min 4.1 s (one Earth rotation relative to stars)
1 decade / century / millennium	10 / 100 / 1,000 years

"Months" in finance and law

30/360 month — used in many bond calculations. Every month is treated as 30 days, every year as 360.
Actual/365 — accruals use actual days elapsed over a 365-day year. Common in money-market and floating-rate notes.
Actual/actual — uses actual days in the period over actual days in the year (366 in leap years). Used in some sovereign bond markets.
Statutory "month" — in many jurisdictions, "one calendar month after 31 January" means the last day of February, not "32 February".

Worked example: weeks to seconds

"How many seconds in a 40-hour work week?" 40 × 3,600 = 144,000 s. Over a 48-week working year that is 6,912,000 s — useful when comparing project effort to subjective time. A career of 40 years × 48 weeks × 40 hours is about 9.95 billion seconds. Conversions like these make abstract durations tangible.

Watch out for the leap second. The International Earth Rotation Service has occasionally inserted a 61st second into the last minute of June or December. Distributed systems that assumed every minute has exactly 60 seconds have famously crashed during these events. Most production systems now use "leap smearing" instead.

Frequently Asked Questions

Using the astronomical year of 365.25 days, there are 31,557,600 seconds in a year. For a common 365-day year, there are 31,536,000 seconds. For a leap year (366 days), there are 31,622,400 seconds.

There are approximately 52.18 weeks in a year (365.25 — 7). A common year has 52 weeks and 1 extra day. A leap year has 52 weeks and 2 extra days. This is why the same date falls on a different day of the week each year.

Earth's orbital period is approximately 365.2422 days. Using 365.25 accounts for the leap year every 4 years (adding 0.25 days per year on average). This Julian year is the standard in astronomy and provides the most accurate average for unit conversions.

A leap year has 366 days by adding February 29th. The Gregorian rule: a year is a leap year if divisible by 4, except century years must also be divisible by 400. This means 2024, 2028, and 2032 are leap years, while 1900 was not but 2000 was.