Convert seconds to years

The second is the SI base unit of time. It is defined by the caesium-133 atomic transition: 9,192,631,770 cycles of this oscillation equal one second. Modern atomic clocks maintain the second to about 10⁻¹⁶ accuracy — you would lose one second in 100 million years.

The Julian year equals 365.25 days — the time for Earth to complete one orbit around the Sun. The Gregorian civil year averages 365.2425 days thanks to the leap-year rule. Most unit conversion uses the Julian value.