Loading...
Loading...
Convert seconds, minutes, hours, days, weeks, months, and years. Instant results for scheduling and calculations.
The second is the SI base unit of time. Since 1967 it has been defined not by astronomy but by atomic physics: one second equals exactly 9,192,631,770 oscillations of the radiation emitted by a caesium-133 atom. This definition makes the second independent of the Earth's rotation, which is gradually slowing and would otherwise cause atomic clocks and calendars to drift apart.
All other time units in common use are multiples of the second. One minute is 60 seconds; one hour is 3,600 seconds; one day is 86,400 seconds. These are not decimal multiples, which is unusual for SI quantities. The 60-based system for minutes and seconds dates back to ancient Babylonian mathematics, and the 24-hour day derives from Egyptian astronomy. No international body has successfully decimalised time.
Months and years are less precise for calculation purposes. A calendar year is 365 days in a common year and 366 in a leap year. For scientific purposes, a Julian year is exactly 365.25 days = 31,557,600 seconds. A mean Gregorian year is 365.2425 days. When this converter shows months, it uses an average of 30.4375 days (365.25 / 12), which is accurate enough for scheduling but not for calendar arithmetic that crosses leap years.
Weeks are always exactly 7 days. This is the one time unit above hours that has no ambiguity across calendars or year lengths.
Time conversion comes up constantly in backend engineering. API rate limits are often expressed in requests per second but quotas are managed per hour or per day. Cache TTLs (time-to-live) are set in seconds in most frameworks, so "cache for 7 days" means setting TTL = 604,800. JWT token expiry, session timeouts, and cron schedule intervals all require mental or programmatic conversion between units.
Unix timestamps count seconds since midnight on 1 January 1970 (the Unix epoch). A timestamp of 1,700,000,000 seconds corresponds to approximately November 2023. When debugging log files, converting a Unix timestamp to a readable date and vice versa is a routine task. The converter above handles the unit arithmetic; a separate date/time calculator handles epoch conversion.
How many seconds are in a day?
Exactly 86,400. A day has 24 hours, each hour has 60 minutes, each minute has 60 seconds: 24 × 60 × 60 = 86,400.
How many seconds are in a year?
A common year (365 days) has 31,536,000 seconds. A leap year (366 days) has 31,622,400 seconds. Using the Julian year average of 365.25 days gives 31,557,600 seconds.
Why does a month have a decimal value in some converters?
Calendar months range from 28 to 31 days, so converting "months" to seconds requires an average. Most converters use 30.4375 days per month (365.25 / 12), which represents the mean Gregorian month. This is accurate for approximate calculations but will differ from actual calendar dates by up to three days.