Unit & Measurement Tables
Time Conversion Table
Time conversion is the one unit family where the small conversions are exact and the large ones are conventions. Seconds to minutes to hours to days to weeks are all defined by fixed integers — 60, 60, 24, 7 — and no ambiguity exists. Months and years are another matter: a month is 28, 29, 30 or 31 days depending on which one you mean, and a year is 365 or 366.
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The convention used throughout this table is the Gregorian mean: a year of 365.2425 days and a month of 30.436 875 days. That is the figure behind every annualised interest rate, every "per month" subscription cost and every actuarial table. Using 30 days for a month instead produces a 1.4% error on an annual figure, and using 365 instead of 365.2425 shifts a long projection by a day every four years.
The other number worth knowing is 2,080. A full-time year is 52 weeks at 40 hours, which is where salary-to-hourly conversions get their divisor. Part-time and overtime work both start from that base, and the tables below include the rows most often needed for payroll and project planning.
Hours to minutes, seconds, days and weeks
| Hours | Minutes | Seconds | Days | Weeks |
|---|---|---|---|---|
| 0.5 | 30 | 1,800 | 0.0208 | 0.003 |
| 1 | 60 | 3,600 | 0.0417 | 0.006 |
| 2 | 120 | 7,200 | 0.0833 | 0.0119 |
| 4 | 240 | 14,400 | 0.1667 | 0.0238 |
| 8 | 480 | 28,800 | 0.3333 | 0.0476 |
| 12 | 720 | 43,200 | 0.5 | 0.0714 |
| 24 | 1,440 | 86,400 | 1 | 0.1429 |
| 40 | 2,400 | 144,000 | 1.6667 | 0.2381 |
| 48 | 2,880 | 172,800 | 2 | 0.2857 |
| 60 | 3,600 | 216,000 | 2.5 | 0.3571 |
| 80 | 4,800 | 288,000 | 3.3333 | 0.4762 |
| 168 | 10,080 | 604,800 | 7 | 1 |
The 168 hour row is one week exactly. A standard full-time year is 2,080 hours, which is 52 weeks at 40 hours.
Days to hours, weeks, months and years
| Days | Hours | Weeks | Months | Years |
|---|---|---|---|---|
| 1 | 24 | 0.1429 | 0.0329 | 0.0027 |
| 7 | 168 | 1 | 0.23 | 0.0192 |
| 14 | 336 | 2 | 0.46 | 0.0383 |
| 21 | 504 | 3 | 0.69 | 0.0575 |
| 30 | 720 | 4.2857 | 0.9856 | 0.0821 |
| 60 | 1,440 | 8.5714 | 1.9713 | 0.1643 |
| 90 | 2,160 | 12.8571 | 2.9569 | 0.2464 |
| 180 | 4,320 | 25.7143 | 5.9139 | 0.4928 |
| 365 | 8,760 | 52.1429 | 11.992 | 0.9993 |
| 730 | 17,520 | 104.2857 | 23.9841 | 1.9987 |
| 1,825 | 43,800 | 260.7143 | 59.9602 | 4.9967 |
Months and years use the Gregorian mean of 30.436 875 days and 365.2425 days. A 30 day month is 0.9856 of the average, which is why February feels short and July does not.
Weeks to days, months and years
| Weeks | Days | Months | Years |
|---|---|---|---|
| 1 | 7 | 0.23 | 0.0192 |
| 2 | 14 | 0.46 | 0.0383 |
| 4 | 28 | 0.9199 | 0.0767 |
| 6 | 42 | 1.3799 | 0.115 |
| 8 | 56 | 1.8399 | 0.1533 |
| 12 | 84 | 2.7598 | 0.23 |
| 16 | 112 | 3.6797 | 0.3066 |
| 26 | 182 | 5.9796 | 0.4983 |
| 52 | 364 | 11.9592 | 0.9966 |
Fifty-two weeks is 364 days, one day short of a common year. That missing day is why the weekday a date falls on drifts by one day each year and by two after a leap year.
Seconds to minutes, hours and days
| Seconds | Minutes | Hours | Days |
|---|---|---|---|
| 30 | 0.5 | 0.0083 | 0.0003 |
| 60 | 1 | 0.0167 | 0.0007 |
| 300 | 5 | 0.0833 | 0.0035 |
| 600 | 10 | 0.1667 | 0.0069 |
| 1,800 | 30 | 0.5 | 0.0208 |
| 3,600 | 60 | 1 | 0.0417 |
| 7,200 | 120 | 2 | 0.0833 |
| 86,400 | 1,440 | 24 | 1 |
86,400 seconds in a day is not quite the length of a solar day. The Earth rotates once in 86,164 seconds of sidereal time; the extra 236 seconds is the amount the planet has to turn to face the sun again.
How to Use These Tables
- Payroll: divide annual salary by 2,080 for the hourly rate, or multiply the hourly rate by 2,080 for the annual figure. $62,400 a year is $30.00 an hour.
- Project planning: multiply working days by 8 for hours, then divide by 5 for weeks. A 90 day project is 720 hours, or 18 working weeks.
- Age and tenure: divide days by 365.2425 for years, not 365. Someone born 10,000 days ago is 27.38 years old.
- Subscription costs: multiply a monthly price by 12 for the annual cost, but divide an annual price by 12.1738 — not 12 — if you want the true monthly equivalent on a Gregorian year.
- Billing cycles: a 30 day cycle is 12.17 cycles per year, so a "monthly" plan charged every 30 days costs 1.4% more per year than one charged on the calendar month.
Common Questions
Why is a month 30.4369 days and not 30?
Because the Gregorian year of 365.2425 days divided by 12 is 30.436 875. A 30 day month would give a 360 day year, which is 5.24 days short. The 360 day year survives only in some accounting conventions.
How many hours are in a work year?
2,080, from 52 weeks × 40 hours. It ignores holidays and paid leave, so the actual hours worked are lower — typically 1,900 to 2,000 in the US once ten holidays and ten vacation days are removed.
Is 52 weeks exactly one year?
No, 52 weeks is 364 days. A common year is 365 and a leap year 366, so a year is 52 weeks and one day, or two in a leap year. That leftover day is why calendars drift.
How do I convert seconds to hours quickly?
Divide by 3,600. For a rough figure, divide by 3,600 twice from seconds — no, that gives hours squared. The reliable mental shortcut is 3,600 seconds an hour and 86,400 a day.
Why are there 86,400 seconds in a day when the Earth takes less to rotate?
A solar day is the time from noon to noon, which is 86,400 seconds on average. A sidereal day, one full rotation against the stars, is 86,164 seconds. The difference exists because the Earth also moves along its orbit.
Does a leap year affect these conversions?
Only at the year scale. The Gregorian mean of 365.2425 days already averages the leap years in, so a multi-year conversion is correct without counting them. Single-date arithmetic does need the actual calendar.
More Unit & Measurement Tables
Sources
- NIST Special Publication 811 — units of time and the second — National Institute of Standards and Technology
- Leap years and the Gregorian calendar — United States Naval Observatory
- Time and frequency from A to Z — the definition of the second — National Institute of Standards and Technology
Filed with Everyday Life calculations.