Time Converter
Convert between time units from picoseconds, nanoseconds and milliseconds through to seconds, minutes, hours, days, weeks, months, years, centuries, millennia and astronomical time scales. This time converter is useful for everyday planning, study, science, engineering, date calculations and understanding very short or very long durations.
Convert time
Choose the starting time unit and the target unit, then enter a value. The calculator converts the input into seconds first, then converts that second value into the selected target unit and into the full conversion table below.
Quick references
Full conversion table
All units converted from your entered value, grouped by category.
Enter a value above to see all conversions.
Date duration calculator
Find the difference between two dates, or add / subtract time from a date.
Date difference
Add or subtract time from a date
Time reference guide
Notable durations — from the blink of an eye to the age of everything.
Conversion facts
How it works
This converter uses seconds as the base unit. When you enter a value, the calculator converts that value into seconds, then divides by the number of seconds in the target unit. This keeps very small units like nanoseconds and very large units like centuries or astronomical years consistent.
Some time units are exact, such as 60 seconds in a minute and 3,600 seconds in an hour. Other units are averages, such as an average month, because calendar months have different lengths. The page labels these average units clearly so the result is easier to interpret.
Formula used
converted value = time in seconds ÷ seconds per target unit
Common reference values include: 1 minute = 60 seconds, 1 hour = 3,600 seconds, 1 day = 86,400 seconds, 1 week = 604,800 seconds, 1 Julian year = 31,557,600 seconds and 1 average month ≈ 2,629,800 seconds.
Worked example
Example: convert 3 hours to seconds
There are 3,600 seconds in 1 hour.
So, 3 hours is 10,800 seconds.
Example: convert 90 days to weeks
There are 7 days in 1 week.
So, 90 days is about 12.86 weeks.
Common mistakes
Treating every month as exact
Months vary from 28 to 31 days. An average month is useful for estimates, but exact calendar work should use actual dates.
Ignoring leap years
A normal year has 365 days, a leap year has 366 days, and a Julian year average is 365.25 days.
Mixing duration and clock time
This converter handles durations. Time zones, daylight saving changes and local clock changes can affect real date/time differences.
Rounding tiny or huge values too early
Nanoseconds, picoseconds and astronomical durations can produce very large or very small numbers, so scientific notation may be more suitable.
Common questions
How many seconds are in a day? ⌄
Why is the month value approximate? ⌄
What is a Julian year? ⌄
Does the date calculator include daylight saving time? ⌄
Sources, assumptions and disclaimer
This converter is for general education, planning, study and everyday time calculations. It uses seconds as the base unit and fixed conversion factors for standard duration units. Some calendar-related values are approximate because real calendar months and years vary.
- Base unit: most conversions are handled through seconds.
- Exact units: seconds, minutes, hours, days and weeks use fixed values.
- Average units: months and some year-style values are approximations for general conversion.
- Date calculations: simple date differences may not capture all time-zone and daylight-saving complexities.
- Astronomical values: long-duration values are simplified for comparison and education.
- Disclaimer: this page does not replace official calendar rules, legal deadline calculations, payroll systems, scientific standards or professional scheduling advice.