How Many Seconds in a Day
Have you ever wondered how many seconds are in a day—or in a week, a year, or even a decade? Rent’s famous lyric tells us there are 525,600 minutes in a year, but that leaves us with a follow-up question: how many seconds is that?
In this guide, I’ll show you exactly how to convert between seconds, minutes, hours, days, weeks, months, years, and beyond. I’ll also provide a handy reference table to make it easier to keep track of all these time conversions.
Plus, if you want a deeper understanding of the question “How many seconds are in a day?”—including why the precise number can vary slightly—read on to learn more about leap seconds, atomic clocks, and how scientists keep our sense of time accurate.
What Is a Second?
A second is the base unit of time we use every day. All other larger (or smaller) units of time—minutes, hours, nanoseconds, etc.—ultimately tie back to the second. Historically, scientists defined a second as 1/86,400 of the average solar day (the time it takes Earth to complete one full rotation on its axis). However, because Earth’s rotation can slow or speed up slightly over long periods, scientists now rely on atomic clocks, which measure the radiation cycles of a cesium-133 atom, to define the second more precisely.
Leap Seconds
Due to tiny changes in Earth’s rotation, timekeepers occasionally add “leap seconds” to our clocks. These leap seconds keep our clocks and calendars aligned with Earth’s real-time motion around the Sun. Although leap seconds are rare, they prevent our timekeeping from drifting enough to affect daily life—if we never corrected that drift, our clocks would eventually be completely out of sync with day and night.
How Many Seconds Are in a Day?
Under normal circumstances, one standard day includes:
- 24 hours per day
- 60 minutes per hour
- 60 seconds per minute
When you multiply 24 × 60 × 60, you get 86,400 seconds. That’s how many seconds are in a typical day. However, if a leap second is added (which might happen on June 30 or December 31 in some years), that particular day would contain 86,401 seconds.
If you want to get even more specific, scientists can calculate variations in the length of a day by measuring Earth’s rotation rate. Those variations are extremely small, but they’re the reason leap seconds exist.
Converting Seconds to Other Time Units
Seconds in a Minute
- 1 minute = 60 seconds.
Our use of 60 seconds per minute dates back to ancient Babylonian math systems, which were based on the number 60.
Seconds in an Hour
- 1 hour = 60 minutes = 60 × 60 = 3,600 seconds.
Multiply the 60 seconds in a minute by the 60 minutes in an hour, and you’ll get 3,600 seconds.
Seconds in a Day
- 1 day = 24 hours = 24 × 3,600 = 86,400 seconds.
(Not counting occasional leap seconds.)
Seconds in a Week
- 1 week = 7 days = 7 × 86,400 = 604,800 seconds.
Seconds in a Month
Months vary between 28 and 31 days. For a quick average:
- 1 average month ≈ 30.42 days.
Multiply 30.42 by 24 hours/day, then by 3,600 seconds/hour to estimate:bashCopyEdit30.42 days × 24 hours/day = 730.08 hours 730.08 hours × 60 minutes/hour = 43,804.8 minutes 43,804.8 minutes × 60 seconds/minute = 2,628,288 seconds (approx.)
If you need the exact number of seconds in a particular month, multiply 24 × 60 × 60 by the actual number of days in that month.
Seconds in a Year
- 1 year = 365 days (common year) = 365 × 86,400 = 31,557,600 seconds.
Many people use the simplified figure 31,536,000 seconds, but 31,557,600 accounts for leap years averaged over a long period (365.25 days). And if you include leap seconds, it can vary by a second or two each year.
Quick Conversions Chart
Below is a table that shows how seconds, minutes, hours, days, weeks, months, years, decades, and centuries compare. (For months, years, decades, and centuries, note that these numbers are averages and can vary with leap years, leap seconds, and the exact length of each month.)
| …in a Second | …in a Minute | …in an Hour | …in a Day | …in a Week | …in a Month (avg) | …in a Year (avg) | …in a Decade (avg) | …in a Century (avg) | |
|---|---|---|---|---|---|---|---|---|---|
| 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 | 1/3,600 | 1/60 | 1 | 24 | 168 | 730.08 | 8,760 | 87,600 | 876,000 |
| Days | 1/86,400 | 1/1,440 | 1/24 | 1 | 7 | 30.42 | 365 | 3,650 | 36,500 |
| Weeks | 1/604,800 | 1/10,080 | 1/168 | 1/7 | 1 | 4.3 | 52 | 520 | 5,200 |
| Months (avg) | 1/2,628,288 | 1/43,804.8 | 1/730.08 | 1/30.42 | 1/4.3 | 1 | 12 | 120 | 1,200 |
| Years (avg) | 1/(3.1536×10^7) | 1/525,600 | 1/8,760 | 1/365 | 1/52 | 1/12 | 1 | 10 | 100 |
| Decades | 1/(3.1536×10^8) | 1/(5.256×10^6) | 1/87,600 | 1/3,650 | 1/520 | 1/120 | 1/10 | 1 | 10 |
| Centuries | 1/(3.1536×10^9) | 1/(5.256×10^7) | 1/876,000 | 1/36,500 | 1/5,200 | 1/1,200 | 1/100 | 1/10 | 1 |
Key Tips for Time Conversions
- 1 Minute = 60 Seconds
- 1 Hour = 60 Minutes
- 1 Day = 24 Hours
- 1 Week = 7 Days
- 1 Year ≈ 365 Days (common year), or 52 Weeks
- 1 Decade = 10 Years
- 1 Century = 10 Decades (100 Years)
Remember that months vary in length, so if you need the exact number of days (or seconds) in a given month, use the month’s actual day count rather than an average.
- To get the average number of days in a month, divide 365 (days in a common year) by 12:36512≈30.42 days per month\frac{365}{12} \approx 30.42 \text{ days per month}12365≈30.42 days per month
- To figure out the average number of weeks in a month, divide 52 (weeks in a year) by 12:5212≈4.3 weeks per month\frac{52}{12} \approx 4.3 \text{ weeks per month}1252≈4.3 weeks per month
Why Knowing How Many Seconds Are in a Day Can Matter
- Time Management: When you break your day into seconds, you start to see how much (or how little!) time you really have for tasks.
- Science and Astronomy: Astronomers, physicists, and satellite engineers rely on precise time calculations, including leap seconds, to keep instruments and data in sync.
- Historical and Cultural Significance: Our modern time system has roots in ancient Babylonian practices, and understanding that background can help us appreciate how we came to adopt 60 seconds and 60 minutes as standard.
Bottom Line:
A standard day contains 86,400 seconds (24 hours × 60 minutes per hour × 60 seconds per minute). If a leap second is added, that day has 86,401 seconds. Even though many of us think of days and weeks without a second thought, these little units add up—and understanding their calculations can give you a deeper appreciation for how we keep track of our time.
