Days to Hours

Months vary, so their hour counts do too: 672 hours in a 28-day February, 696 in a leap-year February, 720 in a 30-day month and 744 in a 31-day month. An ordinary year has 8,760 hours and a leap year 8,784. If you are pricing something by the hour over a month, use the actual number of days rather than an average.

Shipping and support promises mix days and hours. Delivery within 48 hours and delivery in two business days are not the same: an order on Friday afternoon can take until Tuesday under the second rule. To count calendar or working days between two dates, use days between dates.

In places with daylight saving time, the spring change makes one local day 23 hours long and the autumn change makes one 25 hours. Anything computed as days × 24 in local time, such as a rental billed hourly or a medication schedule, can be off by an hour across those weekends. Timestamps in UTC avoid the problem.

Astronomers also use the sidereal day, one rotation of Earth relative to the stars, which lasts about 23 hours 56 minutes 4 seconds. The 24-hour solar day is longer because Earth also moves along its orbit and must turn a little further to bring the sun back to the same spot.

Service level agreements are written as percentages but felt in hours. Over a 30-day month, 99.9% uptime allows 0.72 hours of downtime, about 43 minutes, while 99% allows 7.2 hours. Over a year, 99.9% is 8.76 hours. For the larger step, see weeks to days; the countdown timer shows days and hours to a deadline.