This free time converter turns any value from one unit of time into another. Type a number, choose your units on each side, and the result appears immediately. It works in both directions, so you can type into either box, and it covers 23 units from femtoseconds through to centuries.
One thing worth knowing up front: this is a duration converter. It answers questions like how many minutes are in a day or how many seconds are in three hours. It does not convert clock times between time zones, so if you are trying to work out what 3pm in New York is in London, this is not the tool for that.
How to Use the Time Converter
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Enter your value in either box. Decimals are fine, so 1.5 hours works exactly as you would expect.
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Choose your units using the dropdown beside each box, one for what you have and one for what you want.
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Read the result. There is no button to press. The conversion updates as you type, and typing into the right-hand box converts backwards, which is handy when you want to check an answer both ways.
Common Time Conversions
These are the conversions people look up most often. Every one of them is a single step in the converter above.
| Unit |
Equals |
In seconds |
| 1 minute |
60 seconds |
60 |
| 1 hour |
60 minutes |
3,600 |
| 1 day |
24 hours, or 1,440 minutes |
86,400 |
| 1 week |
7 days, or 168 hours |
604,800 |
| 1 month (mean calendar) |
30.4167 days, or 730 hours |
2,629,800 |
| 1 year (calendar) |
365 days, 8,760 hours, or 525,600 minutes |
31,536,000 |
How Long Is a Month? How Long Is a Year?
Months and years are the awkward ones, because neither has a fixed length. Real months run from 28 to 31 days, and years alternate between 365 and 366. That means every time converter has to pick an assumption, and most of them never tell you which one they picked. Here is ours, stated plainly.
A month in this converter is 30.4167 days. That is 365 divided by 12, the mean calendar month, which spreads the year evenly across twelve months. It is more accurate than the rough 30-day month some converters use, and it is why converting 1 month gives you 730 hours rather than a round 720.
A calendar year here is exactly 365 days, with no leap-year allowance. For most purposes that is the number you want. For long spans it drifts: because a real year is closer to 365.24 days, a 365-day assumption loses roughly a quarter of a day per year, which adds up to about a day every four years. If you are converting a handful of years, the difference is invisible. If you are calculating across decades and precision matters, use the tropical year option, which is 365.242 days and reflects the actual cycle of the seasons.
The 23 Units You Can Convert
Everyday units. Seconds, minutes, hours, days, weeks, months, quarters, and years. These cover almost everything most people need, from working out a project timeline to converting a runtime.
Longer spans. Fortnights, decades, and centuries, for historical spans and long-range planning. A fortnight is exactly 14 days, a decade is 10 years, and a century is 100 years.
Sub-second units. Milliseconds, microseconds, nanoseconds, picoseconds, femtoseconds, and shakes. Developers live in milliseconds, hardware and physics work runs down into nanoseconds and below, and a shake is 10 nanoseconds, a unit borrowed from nuclear physics.
Astronomical units. Sidereal seconds, minutes, hours, and days, plus tropical and sidereal years. These measure time against the stars rather than the sun, and the next section explains why that produces different numbers.
The base unit behind all of these is the second, which is defined not by the Earth's rotation but by the behavior of the caesium atom. If you want the formal version, NIST's definition of the SI second sets it out, and the full set of international SI base units puts it in context.
What Are Sidereal Units, and Why Do They Differ?
A solar day is what your watch measures: the time for the Earth to rotate until the sun returns to the same position in the sky, which averages 24 hours. A sidereal day measures the same rotation against the fixed stars instead, and it comes out about four minutes shorter, at roughly 23 hours and 56 minutes.
The difference exists because the Earth is orbiting the sun while it spins. By the time one full rotation is complete relative to the stars, the planet has also moved a little way along its orbit, so it has to turn slightly further for the sun to line up again. Those extra few minutes each day are the gap between solar and sidereal time. Astronomers use sidereal time because star positions stay fixed against it, which is why the US Naval Observatory's guidance on sidereal time treats it as the working standard for observation.
The same logic applies to years. A sidereal year, 365.256 days, is one full orbit measured against the stars. A tropical year, 365.242 days, tracks the cycle of the seasons from equinox to equinox. Both are in the converter, and unless you are doing astronomy the calendar year is the one you want.
Precision and Very Small Units
The converter carries 12 significant figures, which matters most at the small end. Converting 1 nanosecond into seconds gives 1e-9 rather than rounding away to zero, so the sub-second units stay usable in both directions rather than only working one way.
If you have not seen that notation before, 1e-9 is shorthand for 0.000000001, moving the decimal point nine places left. Very large results use the same shorthand in reverse: 1e15 means a 1 followed by fifteen zeros. Everyday conversions stay in plain numbers, so 2 hours into minutes returns exactly 120, not 120.000000000.
Where Time Conversion Comes Up
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Development work. Timeouts, cache lifetimes, and rate limits are usually specified in seconds or milliseconds, while the requirement you were given is in hours or days.
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Video and audio. Frame timings and clip durations are measured in milliseconds, while running times are quoted in minutes.
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Project and payroll math. Turning hours into working days, or days into weeks, without doing it in your head and getting it wrong.
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Science and astronomy. Sub-second units for lab work, and sidereal units for anything involving the sky.
Related Converters and Guides
For a longer walkthrough with worked examples, read our guide to converting hours, minutes and seconds. If you need to convert something other than time, our length converter and weight converter work exactly the same way, and you can browse the full set in all unit converters.
