Week (wk)

CalendarCurrent unit

Seven days. The seven-day week comes from the ancient Near East and is nearly universal in the modern calendar.

1 week = 604,800 seconds (exactly).

About the week

Nothing in the sky produces a seven-day cycle, which makes the week a human invention with a contested pedigree. Babylonians marked the 7th, 14th, 21st and 28th of the lunar month as special, but that was not a continuous cycle. A continuous seven-day cycle tied to the Sabbath is attested in Judaism by the 6th century BC at the latest, and scholars disagree on whether it was borrowed from Babylon or developed independently. The Romans later used a week named for the Sun, the Moon and the five visible planets, and in AD 321 Emperor Constantine decreed it across the empire.

A week is seven days, or 604,800 seconds, and it divides evenly into neither months nor years, which is why calendars shift against it. The ISO 8601 standard starts each week on Monday and assigns week 1 to the week containing the year's first Thursday, so some years have a week 53. Other societies used different lengths: Rome had an eight-day market cycle, and revolutionary France used a ten-day week from 1793 to 1802. The English word comes from Old English wice, meaning a turn or succession.

Sources: Wikipedia: Week; Wikipedia: ISO week date

Week conversion chart

1 week expressed in every other time unit:

More Calendar units

• month (time)
• year (time)
• common year (time)
• leap year (time)
• decade (time)
• century (time)
• millennium (time)

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