Units of time

Unit	Size	Notes
yoctosecond	10−24 s
zeptosecond	10−21 s
attosecond	10−18 s	shortest time now measurable
femtosecond	10−15 s	pulse time of ultrafast lasers
picosecond	10−12 s
nanosecond	10−9 s	time for molecules to fluoresce
microsecond	10−6 s
millisecond	0.001 s
second	1 s	SI base unit
minute	60 seconds
hour	60 minutes
day	24 hours
week	7 days	Also called sennight
fortnight	14 days	2 weeks
lunar month	27.2–29.5 days	Various definitions of lunar month exist.
month	28–31 days
quarter	3 months
year	12 months
common year	365 days	52 weeks + 1 day
leap year	366 days	52 weeks + 2 days
tropical year	365.24219 days[26]	average
Gregorian year	365.2425 days[27]	average
Olympiad	4 year cycle
lustrum	5 years	Also called pentad
decade	10 years
Indiction	15 year cycle
generation	17–35 years	approximate
jubilee (Biblical)	50 years
century	100 years
millennium	1,000 years
exasecond	1018 s	roughly 32 billion years, more than twice the age of the universe on current estimates
cosmological decade	varies	10 times the length of the previous cosmological decade, with CÐ 1 beginning either 10 seconds or 10 years after the Big Bang, depending on the definition.