# Time converter

> Convert minutes to hours, hours to days, weeks to days and years to seconds, from nanoseconds to millennia, with the 365.2425-day Gregorian year.

Interactive version: https://www.calcopenly.com/conversion/time-converter
Subject: Unit converters

Every time unit is a fixed number of seconds, the SI second being defined by the caesium-133 frequency of 9,192,631,770 Hz. Minutes, hours, days and weeks are exact multiples; a day is 86,400 s. Months and years vary on the calendar, so the converter uses their Gregorian averages: 365.2425 days a year, from 146,097 days per 400 years, and 30.436875 days a month.

The default converts 90 minutes to 1.5 hours. Timesheets are a common use, where decimal hours become minutes: 7.75 h is 7 h 45 min.

Results ignore leap seconds and daylight-saving changes. For the length of a particular month or year, count its calendar days (28 to 31, or 365 or 366) instead of using the average.

## Inputs

- **Value**: A number in the “from” unit, or with its own unit
- **From** (options: nanosecond (ns), microsecond (µs), millisecond (ms), second (s), minute (min), hour (h), day (d), week (wk), fortnight, month (mo), year (yr), decade, century, millennium)
- **To** (options: nanosecond (ns), microsecond (µs), millisecond (ms), second (s), minute (min), hour (h), day (d), week (wk), fortnight, month (mo), year (yr), decade, century, millennium)

## Results

- Converted value — main result
- Conversion
- Conversion factor
- Exactness

## Formula

$$
\begin{gathered} x_{\text{to}} = x_{\text{from}} \times \dfrac{f_{\text{from}}}{f_{\text{to}}} \\ f = \text{one unit expressed in } \text{s} \end{gathered}
$$

## Worked examples

### 90 minutes in hours

- Value: 90 min
- From: minute (min)
- To: hour (h)
- **Converted value: 1.5 h**
- Checked against: 90 / 60 = 1.5

### Average Gregorian year in days

- Value: 1 yr
- From: year (yr)
- To: day (d)
- **Converted value: 365.2425 d**
- Checked against: 146,097 days / 400 years = 365.2425

### 1 week in seconds

- Value: 1 wk
- From: week (wk)
- To: second (s)
- **Converted value: 604,800 s**
- Checked against: 7 × 24 × 3600 = 604,800

### Average month in days

- Value: 1 mo
- From: month (mo)
- To: day (d)
- **Converted value: 30.436875 d**
- Checked against: 365.2425 / 12 = 30.436875

## Questions

### How many seconds are in a year?

31,556,952 s in an average Gregorian year of 365.2425 days, the year this converter uses. A 365-day year has 31,536,000 s and a 366-day leap year 31,622,400 s. Astronomy uses the Julian year of 365.25 days, 31,557,600 s, which is also the year inside the light-year.

### How many days are in a month on average?

30.436875 days. The Gregorian calendar repeats every 400 years with 146,097 days, so a year averages 365.2425 days and a month one twelfth of that. Real months have 28 to 31 days, so use the average for rates and long spans and a calendar for specific dates.

### How do I convert decimal hours to hours and minutes?

Multiply the decimal part by 60: 1.5 h is 1 h 30 min, 7.75 h is 7 h 45 min and 0.1 h is 6 minutes. Going the other way, divide minutes by 60, so 90 min is 1.5 h. A timesheet that records 7 h 45 min as 7.45 understates it by 0.3 h.

### How many weeks are in a year?

52.1775 weeks in an average Gregorian year (365.2425 ÷ 7). A 365-day year is 52 weeks and 1 day, and a leap year 52 weeks and 2 days. Those spare days add up, which is why a weekly payroll has 53 paydays in some years instead of 52.

### Does the converter count leap seconds?

No. Every day here is exactly 86,400 SI seconds. UTC has added 27 leap seconds since 1972, the last on 31 December 2016. In 2022 the General Conference on Weights and Measures (Resolution 4) decided to widen the allowed gap between UTC and Earth-rotation time by 2035, so UTC can run without leap seconds for at least a century.

### How accurate is the time converter?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 4 worked examples whose answers come from independent sources; for example, “90 minutes in hours” is checked against 90 / 60 = 1.5.

### Where does the method come from?

NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors; NIST Handbook 44, Appendix C — General tables of units of measurement; Gregorian calendar: 146,097 days per 400 years (mean year 365.2425 days).

## Sources

- [NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors](https://www.nist.gov/pml/special-publication-811)
- [NIST Handbook 44, Appendix C — General tables of units of measurement](https://www.nist.gov/pml/owm/nist-handbook-44-current-edition)
- Gregorian calendar: 146,097 days per 400 years (mean year 365.2425 days)