Time Unit Converter
Convert between any time units: milliseconds, seconds, minutes, hours, days, weeks, months, years, decades, and centuries.
Time Unit Converter
Calculator
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Formula: Result = Value x (FromUnit_seconds / ToUnit_seconds)
Worked example โ 3.5 days = 302,400 seconds
Formula
Result = Value x (FromUnit_seconds / ToUnit_seconds)
Each time unit has a fixed relationship to seconds (the SI base unit). To convert, multiply the input by the source unit's seconds-per-unit factor, then divide by the target unit's factor. This two-step process works for any pair of time units.
Worked Examples
Example 1: Days to Seconds
Problem:How many seconds are in 3.5 days?
Solution:Convert days to seconds using the factor 86,400 seconds/day: 3.5 days x 86,400 s/day = 302,400 seconds Or step by step: 3.5 x 24 = 84 hours, 84 x 60 = 5,040 minutes, 5,040 x 60 = 302,400 seconds.
Result:3.5 days = 302,400 seconds
Example 2: Weeks to Hours
Problem:Convert 2.5 weeks to hours.
Solution:Convert weeks to hours: 1 week = 7 days x 24 hours = 168 hours 2.5 weeks x 168 hours/week = 420 hours Alternatively: 2.5 x 7 = 17.5 days, 17.5 x 24 = 420 hours.
Result:2.5 weeks = 420 hours
Frequently Asked Questions
How do time unit conversions work?
All time unit conversions use the second as the base unit, since it is the SI (International System of Units) standard for time. To convert between any two time units, first convert the input value to seconds by multiplying by the appropriate factor, then divide by the target unit's factor. For example, to convert 2 hours to minutes: 2 hours times 3600 seconds/hour = 7200 seconds, divided by 60 seconds/minute = 120 minutes.
What is the average length of a month and year?
A Gregorian calendar year averages 365.25 days when accounting for leap years (365 days normally, 366 every 4 years, with century and 400-year corrections). This gives an average month of 30.4375 days (365.25/12). For precise scientific calculations, the Julian year of exactly 365.25 days is often used. These averages are important because actual months range from 28 to 31 days, making exact month-to-day conversions date-dependent.
What are the most common time conversion factors?
The essential conversion factors are: 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 year (average) = 365.25 days = 31,557,600 seconds. For smaller units: 1 second = 1,000 milliseconds = 1,000,000 microseconds = 1,000,000,000 nanoseconds. Memorizing the key factors (60, 24, 7, 365.25) allows you to chain conversions quickly.
How do I convert between very large and very small time units?
For extreme conversions like centuries to milliseconds, use the chain multiplication method. Start from the known factor for each step: 1 century = 100 years = 36,525 days = 876,600 hours = 52,596,000 minutes = 3,155,760,000 seconds = 3,155,760,000,000 milliseconds. Working step by step avoids errors. Alternatively, convert to seconds first (the base unit), then to your target unit in a single division.
Why do 'month' and 'year' conversions give slightly different answers each time I check them?
Unlike seconds, hours, or days, a month and a year are not fixed lengths of time, so any converter must pick an averaging convention. This tool uses 30.4375 days per month and 365.25 days per year, the standard Gregorian averages that account for leap years. A calendar month can actually be 28, 29, 30, or 31 real days, and a specific calendar year is 365 or 366 days, so converting '3 months' to exact days only gives an approximation unless you specify which three calendar months you mean. For legal, financial, or scheduling contexts where the exact number of days matters, use a date calculator that operates on real calendar dates rather than an averaged duration converter.
What is the difference between a solar day and a sidereal day?
A solar day is the 24 hour interval between successive noons, measured against the Sun, and it is the basis for the 86,400 second day used in all civil time conversions. A sidereal day measures one full rotation of the Earth relative to distant stars and runs about 23 hours 56 minutes 4 seconds, roughly four minutes shorter. The gap exists because the Earth also advances along its orbit each day and must turn slightly further to face the Sun again. Astronomical software uses sidereal time for telescope pointing; everything else uses the solar day.
How do leap seconds complicate long time span conversions?
Civil time on the UTC scale is occasionally adjusted by inserting a leap second so that clock time stays closely aligned with the irregular rotation of the Earth. When one is inserted, a single minute contains 61 seconds rather than 60, which breaks the assumption that any interval in days can be multiplied by exactly 86,400 to get seconds. For everyday conversions the effect is negligible, but for precise elapsed time over years, systems generally count on a continuous scale such as TAI and apply the offset only when displaying civil time.
How do I convert decimal hours into hours, minutes and seconds?
Keep the whole number as hours, then multiply the fractional part by 60 to get minutes, and multiply any remaining fraction by 60 again for seconds. For 2.75 hours, 0.75 multiplied by 60 gives 45, so the answer is 2 hours 45 minutes. For 7.42 hours, 0.42 multiplied by 60 gives 25.2 minutes, and 0.2 multiplied by 60 gives 12 seconds, so 7 hours 25 minutes 12 seconds. Timesheets and payroll systems store decimal hours, which is why this split comes up so often.
What is a Julian year and why is it used in astronomy?
A Julian year is defined as exactly 365.25 days of 86,400 seconds each, which is 31,557,600 seconds. It is not a calendar year; it is a fixed unit chosen so that long astronomical intervals convert without depending on where leap days fall, and it is the year used in the definition of the light year. The Gregorian calendar mean year is slightly shorter at 365.2425 days, because the Gregorian rule omits three leap days every four centuries.
How many seconds are in a week, and why is the week an exact conversion?
A week is 7 days, and since a civil day is 86,400 seconds, a week is 604,800 seconds, or 10,080 minutes, or 168 hours. The week converts exactly because it is defined as a whole number of days with no astronomical dependency, unlike the month and the year which must track the Moon and the orbit of the Earth. That exactness is why scheduling systems, sprint planning and payroll cycles built on weeks avoid the drift problems that monthly cycles introduce.
References
Background & Theory
1 minute = 60 seconds, 1 hour = 3,600 seconds and 1 day = 86,400 seconds - all exact. Years are where it stops being exact: a Julian year is 365.25 days by convention, while the Gregorian calendar averages 365.2425 days.
Conversion reference table
| Conversion | Equivalent | Exact or rounded? |
|---|---|---|
| 1 minute | 60 seconds | Exact by definition |
| 1 hour | 60 minutes = 3,600 seconds | Exact |
| 1 day | 24 hours = 86,400 seconds | Exact (SI day) |
| 1 week | 7 days = 604,800 seconds | Exact |
| 1 Julian year | 365.25 days = 31,557,600 seconds | Exact by convention |
| 1 Gregorian mean year | 365.2425 days = 31,556,952 seconds | Exact by convention |
| 1 common calendar year | 365 days = 31,536,000 seconds | Exact |
| 1 fortnight | 14 days = 1,209,600 seconds | Exact |
The second is the SI base unit, defined by fixing the caesium-133 hyperfine transition frequency at exactly 9,192,631,770 hertz. Everything above the day is a calendar convention rather than a physical constant: months range from 28 to 31 days, so "one month" has no fixed length in seconds, and financial contracts get round this by specifying a day-count convention such as 30/360 or actual/365. Astronomy uses the Julian year of exactly 365.25 days, which is why a light-year is defined against it.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator ยท Editorial policy
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