Ever wondered how many seconds there are in a day? How about a week? A year? Thanks to Rent, we might know the number of minutes in a year (525,600), but how many seconds is that?
Whether you’re trying to get even more granular about how you measure a year or you’re just trying to figure out how many seconds are left until summer vacation, this guide will teach you how many seconds are in a day, a week, a year, and beyond. Not only will we teach you how to calculate these problems, but we’ll also give you a handy chart to keep track of them.
Read on to find out how to swap one unit of time for another!
All the numbers on a clock represent different aspects of time, all of which come back to seconds.
What’s a Second?
Before we get into how many seconds there are in a day, let’s talk about what a second is. A second is our base unit of time—base, but not smallest. A base unit is a unit defined on its own terms upon which other units are based. That means that all our other units, such as minutes, hours, nanoseconds, and so on, are all based on seconds. We talk about hours in terms of minutes, but minutes are based on seconds, bringing us back to the base unit.
A second used to be based on the Earth’s rotation cycle, with one second being 1/86,400 of the average solar day. Now that we know more about how the Earth rotates—and that the speed at which it rotates is slowing down—we now use a more accurate method. We base a second off of the radiation cycles of a caesium133 atom, often called an “atomic clock.”
Because our astronomical year varies in length, we also sometimes add “leap seconds” to the clock to keep better time, or we’d eventually end up with time being way off of where it should be. Adding seconds is infrequent, and doesn’t actually change the time—all it does is keep us consistent. But those single leap seconds matter, keeping us on track so that a few missed seconds doesn’t become a missed minute or hour or day over time.
The hands on a clock move in seconds, minutes, and hours, which are all, in some ways, measures of seconds.
How Many Seconds in a Day?
Now that we know what a second really is—an arbitrary measurement of time used to calculate other, larger units of time—we can start thinking about how many it takes to make up all the other time units.
How Many Seconds in a Minute
The largest unit after seconds is a minute. There are 60 seconds in one minute. Why? Nobody’s really sure, but it goes all the way back to ancient Babylon.
How Many Seconds in an Hour
You may already know that there are 60 minutes in an hour, but how many seconds is that? To figure it out, we’ll need to multiply.
60 seconds in one minute and 60 minutes in one hour means that $1 \hour = 60 * 60$. Calculate that out and you’ll find that 1 hour = 3,600 seconds.
How to Calculate Seconds Back and Forth
It takes some memorization, but it’s not hard to calculate seconds into minutes, hours, days, or even years; you can even go in reverse! For example, if you know that something will take 120 seconds but aren’t sure how many minutes that is, you simply divide by 60, the number of seconds in a minute.
Likewise, if you want to know how many seconds are in three days, first you’ll need to calculate how many minutes there are in three days. Three days is 72 hours ($24 \hours * 3 \days$), equivalent to 4,320 minutes ($72 \hours * 60 \minutes$), or 259,200 seconds ($4,320 \minutes * 60 \seconds$).
You can do this for really big numbers, too. How many seconds are in a month? Well, the average month is 30.42 days. A day is 24 hours, so the average month is 730.08 hours ($30.42 \days * 24 \hours$). 730.08 hours is equal to 43,804.8 minutes ($730.08 \hours * 60 \minutes$), or 2,628,288 seconds ($43,804.8 \minutes * 60 \seconds$).
...in a second 
.. in a minute 
...in an hour 
...in a day 
...in a week 
...in a month 
...in a year 
…in a decade 
...in a century 

Seconds 
1 
60 
3,600 
86,400 
604,800 
2,628,288 
3.1536 × $10^7$ 
3.1536 × $10^8$ 
3.1536 × $10^9$ 
Minutes 
$1/60$ 
1 
60 
1,440 
10,080 
43,804.8 
525,600 
5.256 × $10^6$ 
5.256 × $10^7$ 
Hours 
$1/3600$ 
$1/60$ 
1 
24 
168 
730.08 
8,760 
87,600 
876,000 
Days 
$1/86400$ 
$1/1400$ 
$1/24$ 
1 
7 
30.42 
365 
3,650 
36,500 
Weeks 
$1/604800$ 
$1/10080$ 
$1/168$ 
$1/7$ 
1 
4.3 
52 
520 
5,200 
Months 
$1/2628288$ 
$1/43804.8$ 
$1/730.08$ 
$1/30.42$ 
$1/4.3$ 
1 
12 
120 
1,200 
Years 
$1/(3.1536 × 10^7)$ 
$1/525600$ 
$1/87600$ 
$1/365$ 
$1/52$ 
$1/12$ 
1 
10 
100 
Decades 
$1/(3.1536 × 10^8)$ 
$1/(5.256 × 10^6)$ 
$1/3650$ 
$1/520$ 
$1/520$ 
$1/120$ 
$1/10$ 
1 
10 
Centuries 
$1/(3.1536 × 10^9)$ 
$1/(5.256 × 10^7)$ 
$1/876000$ 
$1/36500$ 
$1/5200$ 
$1/1200$ 
$1/100$ 
$1/10$ 
1 
Key Tips for Time Conversions
It’s not a big deal if you can’t memorize this whole table—most people can’t tell you how many seconds are in a decade off the top of their head. But the calculations are simple math—you just need to know the basics!
One Minute = 60 Seconds
One Hour = 60 Minutes
One Day = 24 Hours
One Week = 7 Days
One Year = 52 Weeks
One Decade = 10 Years
One Century = 10 Decades
It can be difficult to figure out how many days or weeks are in a month, because months vary in length between 28 and 31 days. If you find yourself needing to figure things out on a more exact basis, use the number of days in the specific month you’re looking for rather than trying to use an average.
If a specific month won’t work and you just want an overall sense of the number of days in a month, for example, you know that there are 365 days and 12 months in a year. Divide $365/12$ for 30.42, the average number of days in a month. You don’t have to memorize it—just solve it out!
Likewise, you can divide the number of weeks in a year, 52, by the number of months in a year, 12, to get 4.3, the average number of weeks in a month.
What’s Next?
Ready for more big numbers? Check out this guide to how many zeros there are in a billion and beyond!
If you just want to test your calculation skills, these math games are great for fifth graders!
Converting seconds to minutes and beyond requires a solid grasp of multiplication—if you need a little help with memorizing your times tables, our multiplication guide will help you out!
Have friends who also need help with test prep? Share this article!
Melissa Brinks graduated from the University of Washington in 2014 with a Bachelor's in English with a creative writing emphasis. She has spent several years tutoring K12 students in many subjects, including in SAT prep, to help them prepare for their college education.