For companies in the USA from Florida, Maine, Texas, Kentucky to schools in UK all require to know the amount of time each day in minutes or even second or, week in hours, month and ultimately total minutes in year they have to run smoothly.

The Gregorian calendar 365.2425 days in a year is used by most countries that was introduced in October 1582 by Pope Gregory XIII to standardize time making it more accurate. Calculating the hours that are in each year is not straightforward as there’s common years of 365 days and a leap year every 4 years with 366 days.

Gregorian calendar also known as a common year is used by the western world to calculate hours in one year.

**Number of hours in a common year calculation**

First work out the number of hours in a day, days a week, weeks in a year.

24 hours = 1 day, 168 hours = 1 week (24 x 7), 52 weeks = 1 year, 12 months = 1 year

Common year formula multiply number of days in year 365 days x 24 hours a day

**365 x 24 hours =** **8760 hours in a year**. (**Common calendar year**)

**Leap year calculation in hour**

One day is added to February making 29 days every 4 years totaling 366 days.

Leap year formula multiply number of days in leap year x hours in a day

**366 x 24 hours =** **8784 number of hours in a leap year**.

An astronomical year/solar year the earth circulates around the sun and it take about 365 days, 5 hours, 48 minutes & 46 seconds or 365.242189 days; this is the reason a ¼ day is added to account for a leap year every 4 year to 366 days.

**Astronomical year in hour’s calculation**

Multiply number days a year x hours a day x minutes per hour

365 x 24 x 60 minutes = 525,600 minutes

5 hours = 5 x 60 = 300 minutes

**= 525,600 + 300 =** **528,900 hours in an astronomical year**.

Additional 48 minutes and 46 seconds.

**Other calendar years previous used**

Julian calendar, named after Julius Caesar*, *dated from 46BC to 1582 when it was replaced. The calendar added one additional day every four years making up for a leap year with a ¼ day added each year to 365.25 days account for the earth to circle the sun.

Julian year astronomical formula calculation number of days x hours a day

**365.25 days × 24 hours day =** **8766 hours in a Julian year**.

**Sidereal year**

According to Cosmos a Sidereal year is “Sidereal period” is the time it takes for a planet to complete one orbit”.

**365.25636 days × 24 hours/day =** **8766.15264 hours in Sidereal year**.