A day has 86,400 seconds (24 × 60 × 60), a week has 168 hours (604,800 seconds), and a year has 52 weeks plus 1 day, or plus 2 days in a leap year. A 365-day year is 8,760 hours or 31,536,000 seconds, and the Gregorian average year is 52.1775 weeks.
Quick reference: time conversion chart
| Period | Seconds | Minutes | Hours | Days | Weeks |
|---|---|---|---|---|---|
| 1 minute | 60 | 1 | 0.01667 | 0.0006944 | 0.00009921 |
| 1 hour | 3,600 | 60 | 1 | 0.04167 | 0.005952 |
| 1 day | 86,400 | 1,440 | 24 | 1 | 0.1429 |
| 1 week | 604,800 | 10,080 | 168 | 7 | 1 |
| 30-day month | 2,592,000 | 43,200 | 720 | 30 | 4.2857 |
| Average Gregorian month | 2,629,746 | 43,829.1 | 730.485 | 30.4369 | 4.3481 |
| 365-day year | 31,536,000 | 525,600 | 8,760 | 365 | 52.1429 |
| 366-day leap year | 31,622,400 | 527,040 | 8,784 | 366 | 52.2857 |
| Average Gregorian year (365.2425 days) | 31,556,952 | 525,949.2 | 8,765.82 | 365.2425 | 52.1775 |
| Sidereal day (not exact) | 86,164.09 | 1,436.07 | 23.9345 | 0.99727 | 0.1425 |
NIST SP 811 (Appendix B.8) lists the minute as exactly 60 s, the hour as 3,600 s, the day as 86,400 s and the 365-day year as 31,536,000 s; the Gregorian average of 365.2425 days follows from the leap-year rule. The sidereal day is a measured value. Each section below covers one conversion in detail.
How many seconds in a day?
A day has 86,400 seconds: 24 hours × 60 minutes × 60 seconds. NIST lists the day as exactly 8.64 × 10⁴ s, the hour as 3,600 s and the minute as 60 s. A day also has 1,440 minutes. In civil time (UTC) a day with a leap second has 86,401 seconds.
The second is the SI base unit of time, and the hour and minute are defined from it: 1 h = 3,600 s, 1 min = 60 s. So 24 × 3,600 = 86,400.
Seconds in common periods
| Period | Seconds | Minutes | Hours |
|---|---|---|---|
| 1 minute | 60 | 1 | 0.0167 |
| 1 hour | 3,600 | 60 | 1 |
| 1 day | 86,400 | 1,440 | 24 |
| 1 week | 604,800 | 10,080 | 168 |
| 30-day month | 2,592,000 | 43,200 | 720 |
| 365-day year | 31,536,000 | 525,600 | 8,760 |
| 366-day year | 31,622,400 | 527,040 | 8,784 |
NIST lists the 365-day year as exactly 3.1536 × 10⁷ s. Convert other values with seconds to hours, seconds to days, hours to seconds or years to seconds.
Worked examples: seconds in a day
Example 1: a 10-hour shift
10 × 3,600 = 36,000 seconds.
Example 2: seconds to days
1,000,000 seconds ÷ 86,400 = 11.57 days, which is 11 days, 13 hours, 46 minutes and 40 seconds (0.5740 day × 24 = 13.78 h; 0.7778 h × 60 = 46.67 min).
Example 3: seconds left in the day
At 18:30:00, 5.5 hours remain: 5.5 × 3,600 = 19,800 seconds.
Does a day always have 86,400 seconds?
Not in civil time. Earth's rotation is not perfectly steady, and the IERS Earth Orientation Center decides when a second is added to UTC so it stays within 0.9 s of Earth-rotation time (UT1). On such a day the last minute lasts 61 seconds, as on 30 June 2012. The IERS notes that 27 seconds had been added since 1972, the last on 1 January 2017.
A sidereal day, one rotation relative to the stars, is 8.616409 × 10⁴ s in NIST's tables (not exact): 86,164.09 s = 23 h 56 min 4.09 s, which is about 235.9 s shorter than the 86,400 s solar day used for clocks.
Quick ways to remember: seconds in a day
- 24 × 60 × 60 = 86,400.
- A million seconds is about 11.6 days.
- A year is about 31.5 million seconds.
How many hours in a week?
A week has 168 hours: 7 days × 24 hours. That is also 10,080 minutes (168 × 60) and 604,800 seconds (168 × 3,600). NIST's conversion tables define the day as exactly 86,400 seconds and the hour as exactly 3,600 seconds, so all week totals follow by multiplication.
The second is the SI base unit of time. NIST SP 811, Appendix B.8 lists the hour as exactly 3,600 s, the minute as exactly 60 s and the day as exactly 86,400 s. With seven days in a week:
hours = 7 × 24 = 168
minutes = 168 × 60 = 10,080
seconds = 168 × 3,600 = 604,800
Converters: days to weeks, days to hours, hours to minutes and hours to seconds.
Hours in a work week
A standard full-time week is often 40 hours, which is 40 ÷ 168 = 23.8% of all hours in the week. Splitting the rest:
| Use of the week | Hours | Share of 168 |
|---|---|---|
| Work (40 h) | 40 | 23.8% |
| Sleep (8 h × 7) | 56 | 33.3% |
| Everything else | 72 | 42.9% |
The 40 and 8 hours are illustrative figures, not standards. To total hours worked in a week from start and end times, use the hours calculator.
Worked examples: hours in a week
Example 1: total hours in 4 weeks
4 weeks × 168 = 672 hours, which is 40,320 minutes. A project estimated at 100 hours therefore needs 100 ÷ 168 = 0.60 of a full week of continuous time, or 2.5 weeks at 40 hours a week.
Example 2: part-time hours
Working 25 hours a week is 25 ÷ 168 = 14.9% of the week and 1,300 hours over 52 weeks (25 × 52).
Example 3: seconds in a day versus week
86,400 × 7 = 604,800 seconds. A timer set to 1,000,000 seconds runs 1,000,000 ÷ 604,800 = 1.65 weeks, or 11.57 days.
Example 4: converting minutes
A task list totalling 3,600 minutes is 3,600 ÷ 60 = 60 hours, or 2.5 days of 24 hours, or 1.5 work weeks of 40 hours.
Quick reference: hours in a week
- Day: 24 h, 1,440 min, 86,400 s.
- Week: 168 h, 10,080 min, 604,800 s.
- Year: 8,760 h (365 days), 8,784 h (366 days).
- Rule of thumb: a week is about 10,000 minutes (10,080).
For the other everyday measurement questions see the unit converters and the metric vs imperial guide.
How many weeks in a year?
A year has 52 weeks and 1 day in a normal 365-day year (365 ÷ 7 = 52.14) and 52 weeks and 2 days in a 366-day leap year (52.29). Averaged over the Gregorian calendar, whose mean year is 365.2425 days, that is 52.1775 weeks. So "52 weeks" is a rounded figure, never a full year.
A week is 7 days and NIST fixes the day at exactly 86,400 seconds, so a week is 604,800 seconds. The year then divides as follows:
| Year type | Days | Weeks | Weeks + days |
|---|---|---|---|
| Common year | 365 | 52.143 | 52 weeks, 1 day |
| Leap year | 366 | 52.286 | 52 weeks, 2 days |
| Gregorian average | 365.2425 | 52.1775 | about 52 weeks, 1.24 days |
The USNO states the leap-year rule (every year divisible by 4, except centurial years not divisible by 400), which is where the 365.2425 average comes from. For the day-based version of the same math use days to weeks and weeks to years.
Why does one weekday occur 53 times?
52 weeks cover only 364 days. The leftover day (two in a leap year) is an extra copy of the weekday the year starts on. Checked against the calendar:
| Year | Days | Weekday that occurs 53 times |
|---|---|---|
| 2026 | 365 | Thursday (Jan 1 is a Thursday) |
| 2027 | 365 | Friday |
| 2028 | 366 | Saturday and Sunday |
| 2029 | 365 | Monday |
| 2030 | 365 | Tuesday |
Because of the extra day, the same calendar date also moves forward by one weekday each year, and by two in a leap year. This is why some years have 53 Fridays, or why a weekly paycheck lands 53 times in certain years. An hourly worker paid for a 40-hour week earns 52 × 40 = 2,080 hours in a plain 52-week count, but 53 × 40 = 2,120 hours in a 53-week year; see how to calculate hourly rate from salary.
How many weeks are in a month?
Divide the year by 12: 52.1775 ÷ 12 = 4.348 weeks on average, or 30.44 days. February in a common year is exactly 4 weeks (28 days), and a 31-day month is 4.43 weeks. Treating every month as 4 weeks gives only 48 weeks a year, four short of the real count.
Worked examples: weeks in a year
Example 1: weeks until a date
January 1 and December 31 of a 365-day year are 364 days apart, so 364 ÷ 7 = 52 weeks exactly between those two dates. The date duration calculator gives the exact count between any two dates.
Example 2: weekly pay
A yearly amount of 52,000 paid weekly is 52,000 ÷ 52 = 1,000 per week. A 53-payday year changes the per-check figure only if the amount is fixed per year: 52,000 ÷ 53 = 981.13.
Example 3: a 90-day plan
90 ÷ 7 = 12.86, so it is 12 weeks and 6 days.
Quick ways to remember: weeks in a year
- 52 × 7 = 364, so a year is always 1 or 2 days more than 52 weeks.
- Common year: +1 day. Leap year: +2 days.
- For longer spans use 52.18 weeks per year.