How many hours in a year

A year is 8,765.82 hours here: the Gregorian average of 365.2425 days, times 24. That is an average rather than a definition, because a real year is 365 days (8,760 hours) or 366 (8,784), and the leap-year rule is what makes the mean come out at 365.2425. The Julian year of exactly 365.25 days, which astronomers use as a unit, is 8,766 hours. Which is right depends on what the figure is for, and they never differ by more than a day.

Worked through: 1 year x 8,765.82 = 8,765.82 h.

Going the other way, one hour is 0.0001140795 years.

For mental arithmetic: 8,760 for a calendar year. Multiply by 8,766 for an average over many years.

Two very different numbers answer 'hours in a year', and confusing them is expensive. The calendar figure is 8,760, the one engineers use for anything that runs continuously: a power plant's capacity factor is its annual output divided by its rating times 8,760, and an always-on device's annual energy is its wattage times 8,760. The working figure is 2,080 (52 weeks of 40 hours), and it is the standard divisor for turning an annual salary into an hourly rate, so $52,000 a year is $25 an hour. 2,080 is less than a quarter of 8,760. And the working figure is itself a convention: it counts paid holidays as hours worked and ignores the extra weekday that makes some years 2,088 hours.

Precision is worth matching to the input. A measurement given as 0.1 year carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.