Week (wk)
The week is exactly seven days, or 604,800 seconds, and it is one of the most culturally universal units of time on Earth. Unlike the day, month, and year, the week has no astronomical basis — it does not correspond to any observable celestial cycle. Its length is purely conventional, rooted in ancient Mesopotamian tradition and reinforced by religious observance across Judaism, Christianity, and Islam. Despite having no scientific rationale, the seven-day week is the one unit of time that has never been successfully reformed. The French Revolution's attempt to replace it with a ten-day week failed within years, and the Soviet Union's experiments with five- and six-day weeks in the 1930s were similarly abandoned.
Definition
One week equals exactly 7 days, 168 hours, 10,080 minutes, or 604,800 seconds. One year of 365 days contains 52 weeks and one day. One year of 366 days (leap year) contains 52 weeks and two days.
History
The seven-day week originated in ancient Mesopotamia, where each day was associated with one of the seven celestial bodies visible to the naked eye: the Sun, Moon, Mars, Mercury, Jupiter, Venus, and Saturn. This system was adopted into Hebrew culture, where the seventh day became the Sabbath — a day of rest prescribed in the Torah. The week spread through the Roman world during the first centuries of the Common Era, initially through astrological influence and later through the spread of Christianity, which adopted the seven-day structure with Sunday as the day of worship. By the time of Emperor Constantine in the fourth century, the seven-day week had become standard across the Roman Empire and its cultural heirs. The names of the days in English reflect the original planetary associations filtered through Germanic and Norse mythology: Sunday for the Sun, Monday for the Moon, Tuesday for Tiw (Mars), Wednesday for Woden (Mercury), Thursday for Thor (Jupiter), Friday for Frigg (Venus), and Saturday for Saturn.
Common Uses
The week is the primary unit of work scheduling in most cultures. The standard working week is typically five days in most countries, with two days designated for rest and leisure. Project management tools use weeks as a planning unit: deadlines are set in weeks, sprints in agile software development run one or two weeks, and academic semesters are measured in weeks. Subscription services bill weekly or every four weeks. In medicine, pregnancy is tracked in weeks from conception: a full-term pregnancy is 40 weeks. Clinical trials and vaccine protocols specify dosing schedules in weeks. Sports leagues organize their seasons in weekly rounds or matchdays.
Did You Know? Facts About Week
- The seven-day week is the only major unit of time that has no astronomical basis. Days, months, and years all correspond roughly to astronomical cycles, but the week is purely a human convention. This has made it remarkably durable: it has persisted across calendar reforms, empire collapses, and religious changes for at least 2,500 years.
- The French Revolutionary calendar of 1792 replaced the seven-day week with a ten-day décade. Workers had one day of rest in ten instead of one in seven, which was deeply unpopular. Napoleon abolished the system in 1806, and the traditional week immediately reasserted itself.
- The Soviet Union experimented with both five-day and six-day weeks from 1929 to 1940, partly to keep factories running continuously and partly to weaken religious observance by ensuring that days off fell on different days for different workers. The experiment disrupted family and social life so severely that Stalin ordered a return to the seven-day week in 1940.
- ISO 8601, the international standard for dates and times, defines weeks as starting on Monday and numbers each week of the year from 1 to 52 or 53. Week 1 is the week containing the first Thursday of the year.
- In many languages, the days of the week are named after planets and gods that reveal the week's Babylonian origins. German preserves some: Samstag for Saturday (Saturn's day via Hebrew Shabbat) and Sonntag and Montag for Sunday and Monday directly.