Time Converter: Seconds, Minutes, Hours, Days, Weeks, Months, Years

1. Pick the From unit your time is in, for example hours.
2. Pick the To unit you want, for example weeks.
3. Type the value. The result, the factor and a table of every unit update at once.
4. If you use months, years or decades, check the year basis. The default is the Gregorian average of 365.2425 days.

This table is built live from the value you typed. It shows the same duration in all nine units, so you do not need a second conversion.

The second is the SI base unit of time. The BIPM defines it by fixing the caesium-133 hyperfine transition frequency at exactly 9 192 631 770 Hz. NIST SP 811 then sets the minute at 60 s, the hour at 3,600 s and the day at 86,400 s. Those are fixed numbers, so any conversion among them is exact.

The week is also fixed here: 7 days, or 604,800 s. Months and years are different. A calendar month runs 28, 29, 30 or 31 days. A calendar year runs 365 or 366 days. No single number is true for every month or year.

To convert them anyway, you need an average. This page defines the average month and year in the open, so you can see exactly what is assumed.

Every unit is stored as a whole number of milliseconds. A conversion multiplies by the From length and divides by the To length. Nothing is rounded until the answer is shown.

1. Look up the length of the From unit in milliseconds. One hour is 3,600,000 ms.
2. Look up the length of the To unit. One week is 604,800,000 ms.
3. Divide the first by the second to get the factor: 3,600,000 / 604,800,000 = 1/168. So hours to weeks is hours / 168.
4. Multiply your value by the factor.

With the default basis, the table below gives the factor for every pair. Read across: one of the row unit equals the number shown in each column unit.

The three year bases change only the rows and columns that involve months, years or decades:

Hours to weeks. Divide by 168. Then 100 h / 168 = 0.595238 wk. That is 4 weeks and 4 days, since 0.595 x 7 = 4.17 days.

Seconds to days. A million seconds is 1,000,000 / 86,400 = 11.574074 d. In plain units that is 11 days, 13 hours, 46 minutes and 40 seconds.

Seconds to months. With the Gregorian average, 1,000,000 s is 1,000,000 / 2,629,746 = 0.380265 months. With the Julian year it is 0.380257. The two differ in the fifth digit, which is the cost of choosing an average.

Days to months. Ninety days is 90 / 30.436875 = 2.9569 months, a little under 3. A real span from 1 January to 1 April is 90 days in 2026 and 91 days in 2028, so the calendar count and the average disagree by design.

Years to seconds. One Gregorian-average year is 365.2425 x 86,400 = 31,556,952 s. The Julian year gives 31,557,600 s, and a 365-day year gives 31,536,000 s.

Weeks to years. Fifty-two weeks is 364 days. On the Julian basis that is 364 / 365.25 = 0.996578 yr; on the Gregorian basis it is 0.996598 yr. Either way, 52 weeks falls short of a full year by about a day.

Hours to years. A 10,000 hour goal is 1.1408 years of non-stop hours on the Gregorian basis. It is not a figure for working years, which have far fewer hours.

The Year Basis

The only real choice is how long a year is. The Gregorian average of 365.2425 days is the default because it is the long-run length of the civil calendar. The Julian year of 365.25 days is a round figure used by astronomers and by some converters. A 365-day year is the NIST "year (365 days)", with no leap days at all.

Months Follow the Year

One month is one twelfth of the year you picked. With the Gregorian average it is 30.436875 days, or 2,629,746 s. It is not the 30-day month used in some billing rules.

Leap Seconds Are Ignored

A day here is exactly 86,400 s. Real UTC days have occasionally had an added leap second. That is far too small to matter for everyday conversions.

Round-off at the End

The tool keeps full precision and rounds only the display. If you copy a rounded number and convert again, small errors can build up.

There are three ways to measure a long span. They answer different questions, and mixing them is the most common source of wrong answers.

For calendar time, use a tool that counts real dates. The Date Calculator works out the exact days between two dates, and Months From Today adds real calendar months to a start date. The twelve months of 2026 run 28 to 31 days and add up to 365, while 2028 adds up to 366.

Use This Converter

Pick it when you need an unusual pair, such as seconds to months or years to minutes, when you want a value in all units at once, or when you need to choose the year basis.

Use a Direct Pair Page

For the most common pairs, the dedicated pages give a short answer, a quick table and a focused guide. The links below go to those pages. Where months or years appear they use the Julian year of 365.25 days, so choose the Julian basis here to match them.

Use a Calendar Tool

For dates, ages, project deadlines and business days, count real dates. The Date Calculator and Months From Today pages above do that. This converter cannot know which months your span crosses.

1. Treating a Month as 30 Days

Thirty days is neither the average (30.436875) nor the length of any calendar month except April, June, September and November. A year of twelve 30-day months is only 360 days.

2. Treating 52 Weeks as a Year

Fifty-two weeks is 364 days, one or two days short of a calendar year. Pay or schedules per year can drift by a day.

3. Mixing Decimal Hours with Hours and Minutes

One and a half hours is 1.5 h, which is 1 h 30 min. It is not 1.30 h. Convert minutes by dividing by 60.

4. Using a Rounded Factor in a Chain

Rounding 0.0166667 for minutes to hours and then multiplying by a large number grows the error. Keep the exact fraction 1/60.

5. Comparing Different Year Bases

A result using 365.25 days and one using 365.2425 days differ by about 0.002 percent. That is harmless for a rough figure but not for a table that must match another source exactly.

6. Using an Average for a Deadline

A contract that runs three calendar months from 1 January ends on a date, not after 91.31 days. Count dates when a date matters.

Fixed-unit conversions are exact. Average-unit conversions are exact on the stated basis but are not calendar spans.

On the Gregorian average, 31,556,952 s. A 365-day year has 31,536,000 s and a Julian year has 31,557,600 s. Pick the basis that matches your source.

A calendar month has 28 to 31 days, so there is no single answer. The Gregorian average is 30.436875 days, which is a year of 365.2425 days divided by 12.

The Gregorian calendar repeats every 400 years, and those 400 years hold 146,097 days. Dividing 146,097 by 400 gives 365.2425. NASA reprints this from the Explanatory Supplement to the Astronomical Almanac.

Divide the hours by 168, because a week has 7 x 24 hours. For example, 336 hours is 2 weeks and 100 hours is about 0.595 weeks.

Multiply by 60. For example, 7.5 minutes is 450 seconds. To go back, divide the seconds by 60.

Yes, in this tool. A day is 86,400 s, a week is 7 days and an hour is 3,600 s. Real UTC days that held a leap second are not modelled.

They may use another year basis. Some use 365.25 days, others 365 days or a 30-day month. Change the year basis above to match.

On the Gregorian average, 365.2425 / 7 = 52.1775 weeks. On the Julian year it is 52.1786 weeks. Both are a little over 52.

Here a decade is exactly 10 average years. A real decade holds 3,652 or 3,653 days, depending on its leap years.

Use a calendar tool for that. A deadline in months falls on a date, and the average month cannot say which date. See the Date Calculator and Months From Today.

• The second: SI base unit of time and the caesium frequency 9 192 631 770 Hz (BIPM, SI base units; read 2026-10-03).
• Conversion factors: minute, hour, day and year (365 days) in seconds (NIST SP 811, Appendix B.8; read 2026-10-03).
• SI units for time: the second and the fixed caesium value (NIST Office of Weights and Measures; read 2026-10-03).
• Gregorian calendar: 400-year cycle of 146,097 days and 365.2425-day average (NASA Eclipse Web Site, Doggett, from the Explanatory Supplement to the Astronomical Almanac; read 2026-10-03).