Time conversions

Time converter for SI and calendar units — seconds, milliseconds, minutes, hours, days, weeks, months, years, decades and centuries. Note: month and year conversions use the Julian-year average (365.25 days) and a standardised 30.44-day month.

10 units90 conversion tools📊 See comparison matrix →

s ms min h d wk mo yr dec c

Second conversions

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The SI base unit of time — defined by atomic caesium transitions

Second to Millisecond

Millisecond conversions

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The computing and networking time unit — 0.001 second

Millisecond to Second

1 ms = 0.001 s

Millisecond to Minute

Millisecond to Decade

1 ms = 3.1688e-12 dec

Millisecond to Century

1 ms = 3.1688e-13 c

min

Minute conversions

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Everyday time unit — 60 seconds exactly

Minute to Second

1 min = 60 s

Minute to Millisecond

1 min = 1.9013e-7 dec

Minute to Century

1 min = 1.9013e-8 c

Hour conversions

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The core scheduling unit — 60 minutes or 3600 seconds

Day conversions

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Earth's rotation period — 86,400 seconds

Week conversions

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The 7-day cycle used by all major calendars

Week to Second

1 wk = 604,800 s

Week to Millisecond

1 wk = 604,800,000 ms

Month conversions

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Average month length — 30.44 days (Julian year ÷ 12)

Month to Second

1 mo = 2,629,746 s

Month to Millisecond

1 mo = 2,629,746,000 ms

Year conversions

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Earth's orbital period — 365.25 days (Julian year)

Year to Second

1 yr = 31,557,600 s

Year to Millisecond

1 yr = 31,557,600,000 ms

dec

Decade conversions

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Ten years — used in historical and cultural contexts

Decade to Second

1 dec = 315,576,000 s

Decade to Millisecond

1 dec = 315,576,000,000 ms

Decade to Minute

1 dec = 5,259,600 min

Century conversions

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One hundred years — historical and cultural context

Century to Second

1 c = 3,155,760,000 s

Century to Millisecond

1 c = 3,155,760,000,000 ms

Tips for time conversions

The second is the only SI base unit of time. Longer units (minute, hour, day) are all defined in seconds.

A month is ambiguous: calendar months range from 28 to 31 days. For calculations use 30.44 days (year ÷ 12).

A year in daily life is 365 days, but astronomers and engineers use 365.25 days (the Julian year) to account for leap years.

Millisecond (ms) and microsecond (µs) are essential in networking and computing — but quickly diverge in everyday conversation.

Common mistakes to avoid

Assuming a month is always 30 days — January has 31, February has 28/29.

Confusing seconds of time with seconds of angle (both use "s" abbreviation).

Converting years to days with 360 (financial convention) instead of 365.25 (physical).

Using calendar months for precise durations — use days for accuracy.

Learn about each unit

Full encyclopedia page for every time unit — definition, history, uses, tips.

What is a second?

What is a millisecond?

Time conversion FAQ

Why is a minute 60 seconds instead of 100?

The base-60 (sexagesimal) system comes from ancient Babylonian astronomy (c. 2000 BC). It was chosen because 60 has many divisors (1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30), making fractional calculations easy without decimals. The system survived because it works well for angle and time.

How long is a "month" in mathematical conversions?

A calendar month is 28 to 31 days. For consistency in calculations, the average is 30.4375 days (365.25 ÷ 12) or 30.44 days rounded. Financial calculations sometimes use 30 days/month as a convention. Always specify which "month" you mean.

What is the difference between a year and a Julian year?

A common civil year is 365 or 366 days (with leap year). A Julian year is exactly 365.25 days — used in astronomy and for conversions. The Gregorian year averages 365.2425 days (the basis of our calendar). For most unit conversions, 365.25 days is the standard.