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Convert Millitary Time To Standard Time




Military time, also known as a 24-hour clock, can be hard to understand for people who are used to reading a 12-hour clock. A 24-hour clock represents the hour of the day as a number between 0-23 instead of representing time with two 12-hour periods that are designated AM and PM, 24-hour clocks are useful because they can represent time unambiguously, as each of the 24 hours of the day has a distinct number associated with it.

The 24-hour clock is the most commonly used clock in the world, however, most English-speaking counties opt to use a 12-hour clock instead. In English-speaking countries like the U.S. or Canada, the term “military time” is synonymous with the 24-hour clock as it is the clock used by their respective military organizations.

The men and women who serve in our military have won for us every hour we live in freedom, sometimes at the expense of the very hours of the lifetimes they had hoped to live. – Bob Riley

What Is a 24-Hour Clock (Military Time)?

Credit: WikiCommons

24-hour clocks are a designating the time throughout the 24-hour day. In short, times represented with a 24-hour clock are written in the form hh:mm:ss, where hh is the number of hours that have elapsed since midnight, mm is the number of minutes elapsed from the last hour, and ss is the number of seconds elapsed from the last minute. On the 24-hour clock, an hour designation of 00 corresponds to midnight. Thus, a time reading of 00:00:00 on the 24-hour clock corresponds to exactly midnight—the beginning of a new day. Each consecutive hour is designated by the next consecutive number, 1, 2, 3, etc. The minutes place and seconds place on the 24-hour clock behave exactly as they do on the 12-hour clock, each consisting of 60 divisions labeled with numbers between 0-59.

Since the 24-hour clock consists of one full cycle of 24 hours, the times designated by 00:00 and 24:00 are technically the same—midnight. In order to avoid confusion, rarely is the hour place ever written as 24; the minute after 23:59 the clock snaps back to 00:00 and the cycle starts again. In some rare cases, times with an hour designation greater than 24 will be used to signify late night programming, or in places where business hours commonly exceed midnight. For instance, a time of 26:00 might be used to represent the closing time of a bar that stays open until 2:00 AM.

What Is The Purpose Of Military Time?

The advantage of the 24-hour clock is that it unambiguously distinguishes between daytime and nighttime in its division of hours. Unlike the 12-hour clock, on the 24-hour clock, each day is associated with a unique number instead of a number and a designation of AM or PM. So, a time of 00:00 on a 24-hour clock is unambiguously midnight, where on a 12-hour clock, 12:00 could mean midnight or noon, depending on if it is AM or PM. This lack of ambiguity is why the 24-hour clock is the preferred method of timekeeping for military organizations. Military operations rely on precise temporal coordination of units, and a 24-hour clock prevents any sort of ambiguity in the reporting of times. Instead of reporting the time as 9:00 PM, the time would be reported as the much less ambiguous 21:00.

In the context of military operations, making sure that the actions of all units are temporally synchronized is of the utmost importance. Even the slightest ambiguity in the designation of time can cause problems where units become desynchronized, which can compromise strategy and security. Tracking time using a 24-hour system instead of a 12-hour system ensures that there is no miscommunication and that times can be communicated completely unambiguously.

How To Convert Between 12-Hour Clock And Military Time

From AM/PM To 24-Hour Clock

Converting between AM/PM time and military time is easy. If your time on the 12-hour clock falls in the AM range, then the corresponding designation in military time is the same number. Thus, 7:00 AM is equal to 07:00 in military time. Likewise, 10:27 AM is just 10:27.

If your time on the 12-hour clock is in the PM range, then just add 12 to the hours number to get the corresponding military time designation. So a time of 4:00 PM would be 16:00 in military time. 9:00 PM would be 21:00 and 11:59 PM would be 23:59 in military time. In military time, a time of 24:00 would be the same as 00:00 (midnight), so in most cases 00:00 is used instead of 24:00 to avoid confusion.

From 24-Hour Clock To AM/PM

Converting from military time to AM/PM time is similar to the converse. If your military time hour designation is less than or equal to 12, then the matching 12-hour clock hour designation is the same number. If your hour designation is 13 or greater, then subtract 12 to get the AM/PM hour designation.

Here is a table of all the AM/PM times and their appropriate military time conversions:

Civilian TimeConverts ToMilitary Time
12:00 AM 00:00
1:00 AM 01:00
2:00 AM 02:00
3:00 AM 03:00
4:00 AM 04:00
5:00 AM 05:00
6:00 AM 06:00
7:00 AM 07:00
8:00 AM 08:00
9:00 AM 09:00
10:00 AM 10:00
11:00 AM 11:00
12:00 PM 12:00
1:00 PM 13:00
2:00 PM 14:00
3:00 PM 15:00
4:00 PM 16:00
5:00 PM 17:00
6:00 PM 18:00
7:00 PM 19:00
8:00 PM 20:00
9:00 PM 21:00
10:00 PM 22:00
11:00 PM 23:00

Uses of 24-Hour Clock

Everyday Use

Most official national governments have adopted a 24-hour clock for purposes of government planning and military operation. However, even in countries where a 24-hour clock is the national standard, 12-hour clocks may still be used in certain contexts.

In many countries, like France for instance, the 24-hour clock is the timekeeping convention encountered in everyday life. Movie times, train schedules, work schedules, digital clocks, business hours, and scientific organizations all use 24-hour clocks, and it is common to give the time in terms of its 24-hour designation. The French when speaking of 16:00 will say “le seizième heure” which literally translate in English to “the sixteenth hour.”

Credit: Pixabay

In countries where 12-hour clocks are still predominant, many institutions have adopted 24-hour clocks for precision and ease of communication. In the US and Canada, the term “military time” is synonymous with the 24-hour clock. In American and Canadian English, times are almost always given in 12-hour notation, so specialist areas (aviation, navigation, communications, hospitals, emergency services) use a 24-hour clock in fields where the ambiguities of 12-hour clocks can be dangerous or inefficient.

The use of a 12-hour or 24-hour clock also depends on the device being used to represent the time. Circular analog clocks almost always are numbered 1-12, as there is rarely enough space to comfortably fit 24 equal divisions around the circle. The presence of a larger number of smaller divisions would also make the analog clock more likely drift and become inaccurate over time. As such, most analog clocks have a circular face with only 12 divisions and complete two complete rotations a day. In contrast, digital clocks in countries that have officially adopted 24-hour clocks most always represent the hour with some number 0-23.

Clock And Timekeeping Technology

In terms of technology, virtually all modern technology that requires the use a clock uses a 24-hour layout. Computers, GPS devices, cell phones, and other appliances use 24-hour time notation to both represent the time to users and to internally regulate functions related to time. Most computer OS platforms, like Microsoft Windows or Mac, will only default to a 12-hour clock system only when the computer is set for certain regions/languages. One of the advantages of using 24-hour clocks in computing technologies is to have a single temporal format for device communication.

Credit: Flickr / slgckgc

Storing time in a 24-hour format is more memory efficient than storing it in AM/PM format. 24-hour time only requires a register to store the hour, corresponding to a number between 0-23. Storing time in AM/PM form require another register that contains the AM/PM value. Although not a huge difference, over long run times the added memory required by AM/PM time representation can slow computations. 24-hour time values are unambiguous and can be computed much quicker without an extra register value for AM or PM.

Military Time Convention

The 24-hour clock agreed upon by the American and Canadian armed forces differs in some respects from other usages of a 24-hour clock. Generally, military time is reported without any colons separating the hours and minutes (e.g. 0500 instead of 05:00) and all leading zeros are pronounced. So, a military time of 0530 would be read as “zero-five thirty.” Times that fall on the hour are referred to by “hundred”, so 0100 would be “zero one hundred hours,” 1600 would be “sixteen hundred hours,” and 2300 would be “twenty-three hundred hours.”

Military times are often accompanied by a letter to indicate the time zone. American and Canadian military times assign each time zone a letter and name corresponding to the NATO phonetic alphabet. Starting at the prime meridian in Greenwich, England and going East, the time zones are named and lettered “A” through “M” (“Alfa” through “Mike”) for those time zones that have a positive UTC offset, until reaching the International Date Line. After the line, come the names from “N” through “Y” (“November” to “Yankee”) to designate those time zones with a negative UTC offset. In standard military jargon, the letter Z represents Universal Coordinated Time and so is sometimes called “Zulu time.” Due to historical reasons, the letter “J” is omitted from time zone designations.

The different names, letters,- and corresponding UTC offsets for the military time zones are as follows:

  • Alfa: A +1
  • Bravo: B +2
  • Charlie: C +3
  • Delta: D +4
  • Echo: E +5
  • Foxtrot: F +6
  • Golf: G +7
  • Hotel: H +8
  • India: I +9
  • Kilo: K +10
  • Lima: L +11
  • Mike: M +12
  • November: N -1
  • Oscar; O -2
  • Papa: P -3
  • Quebec: Q -4
  • Romeo: R -5
  • Sierra: S -6
  • Tango: T -7
  • uniform: U -8
  • Victor: V -9
  • Whiskey: W -10
  • X-ray: X -11
  • Yankee: Y -12
  • Zulu: Z 0

History Of The 24-Hour Clock (Military Time)

Ancient Egyptians

The origins of the 24-hour clock trace back to the origins of civilization itself with the ancient Egyptians. The Egyptians used a clock based on the periodic procession of certain constellations across the night sky. They called these constellations the “decans” and each Egyptian hour corresponded with the rising of a decan above the visible horizon.

Originally, the Egyptians had a daily clock that consisted off 36 decans. the rising and falling of these decans were used by the ancient Egyptians to measure both hours of the day and days of the year. The Egyptian year was divided into 36 10-day periods, each 10-day period corresponding to the procession of the decans across the sky beginning with a different one of the 36 decans. This gave the Egyptian decan calendar a  360, with 5 extra days added to give a grand total of 365, remarkably close to our modern day length of a year. Over time, The Egyptians condensed their 36 decan calendar to 24 equal hours, thus giving birth to the first 24-hour clocks. The first written records on decans date back to 2100 BCE where they have been found etched on the backs of coffin lids.

A fragment of half an Egyptian sundial. The half has 12 divisions, corresponding to half the hours in a day.  Credit: WikiCommons

Originally, the division of the day into 24-hour was based on the duration of sunlight during the seasons. The result was that during different seasons,  the lengths of an hour could actually differ, depending on how much light was present.

The ancient Chinese also had an understanding of a 24-hour clock. Initially, the Chinese divided the full day into 12 equal units of duration called “shí,” with each shí corresponding to about 2 modern hours. Starting at the end of the Tang dynasty in the 10-century AD, each shí was divided in half, into 24 equal units of time that roughly correspond to the 24-hours of the modern calendar. Although modern China has shifted to UTC designation, they still use the traditional units of time in many written and ceremonial documents. In Chinese shí is still used to designate 1 hour, though the words xioáshí and shíchen are used to refer to the old designation of a shí as one-twelfth of the day and the newer designation of shí as 1/24th of the day.

Hipparchus

A bust of Hipparchus. Credit: WikiCommons

In the 2nd century BC, the Greek naturalist Hipparchus invented the concept of equinoctial hours—hours that stay the same duration regardless of the duration of light. Hipparchus based his system of 24 equal division of time on his meticulous observations of the periodic orbits of the sun, moon, and stars. Various other calendars based on the motion of the moon were inaccurate as they did not take into account the fact that the moon moves at different rates during different parts of its orbit.

I have composed a book on the length of the year in which I show that the tropical year contains 365 days plus a fraction of a day which is not exactly 1⁄4 day as the mathematicians-astronomers suppose, but which is less than 1⁄4 by about 1⁄300. – Hipparchus

Hipparchus was the first to account for the differing motion of the moon to create a single comprehensive calendar that was exceedingly accurate, even by modern standards. To put the matter in perspective, Hipparchus’ 24-hour cycle faced an offset of approximately 0.1 seconds every 345 years. His same observations of the sun and moons’ movement allowed him to develop the first reliable method for predicting solar and lunar eclipses.

24-Hour Clock In The Middle Ages And Renaissance

As time went on, the 24-hour clock was disseminated into various cultures, though many groups had their own variations of the 24-hour clock or instead opted for a 12-hour clock based on a division between daytime and nighttime. An understanding of the complex nuances of a 24-hour clock and its calculations were confined to institutions of higher learning; most uneducated commoners did not have any sophisticated understanding of the astronomy behind timekeeping devices. Often, local communities had their own way of keeping time that was not based on any well-defined standard. During the Middle Ages, for example, it would have been common to find two villages that had completely different definitions for an hour or hours that would change duration depending on the time of year. During this time period, rarely did people engage in endeavors that required a precise way of keeping time or coordinating a standard with others.

The very first publicly available mechanical clocks were 24-hour clocks made in Italy during the 16th and 17th centuries. These clocks consisted of a single circular face divided into 24 equal arcs that the hour hand would sweep over in one day. At each hour interval, the clocks would ring bells to signify the time change. Early versions of these clocks were very prone to mechanical breakage; the division of the clock face into 24-hours meant that the clock would have to ring over 300 times in one day. This would wear out any rope and pulley mechanisms, so many clock distributors simplified these models into 12-hour clocks that repeated 2 times a day or even 6-hour clocks that repeated 4 times a day.

Military Time In The Industrial Age

Worldwide acceptance of 24-hour clocks as a standard measure of time did not come about until the 18th and 19th century with the advent of trains and the railroad. With the construction of railroads, for the first time, humans had a serious commercial need for accurate clocks that would keep a universal time for scheduling train departures and arrivals. For example, many isolated communities would use their own idiosyncratic clocks that were not set to any standard measure. The result of so many different communities using different clocks led to difficulties in establishing universal train schedules because 3 o’clock in one town might not be 3 o’clock elsewhere.

At the time, different railway companies used different time conventions. The incommensurability of these conventions led to scheduling difficulties, where trains based out of New York worked on New York time, trains out of Chicago on Chicago time, etc. The increased need for accurate time-keeping devices for use on the railroads saw the explosive development of new types of clocks meant to be as accurate as possible over a 24-hour time. Incidentally, the conceptual problems that arise from trying to synchronize two distant clocks were the impetus that led Albert Einstein to develop his Special Theory of Relativity.

The first steps towards an internationally recognized 24-hour clock began in 1876 when the Scottish engineer Sir Sanford Fleming missed a train to Ireland due to an error on train timetables that listed the departure time as PM instead of AM. In response, Sir Fleming suggested proposed a single 24-hour clock for the entire world, based on the time of a single clock located at a universally recognized meridian.

the 24-hour clock located at Greenwich, England. Credit: WikiCommons

At the International Meridian Conference 1884, several international bodies agreed to use Fleming’s clock as a universally recognized standard, and the 24-hour clock was officially adopted for international use and the meridian running through the town of Greenwich, England was agreed to be the international standard from which the passage of the days on Earth were to be measured. In 1886, the Canadian Pacific Railway became one of the first commercial organizations to officially adopt the 24-hour clock. This was the precursor to modern-day Coordinated Universal Time (UTC), which is used to synchronize global communications and transport.

By the beginning of the 20th century, most Western nations had adopted and were beginning to adopt 24-hour clocks as national standards.  During WWI, Great Britain adopted the 24-hour clock as the standard military convention, though the public sphere continued to use the more familiar 12 hour AM/PM clock. The US military did not adopt the 24-hour clock as standard until 1942, shortly after their entrance into WWII.

Modern Day Usage Of Military Time

Nowadays, almost all non-English speaking nations have adopted some version of a 24-hour clock for governmental and everyday life purposes. Often, countries integrate both 24- and 12-hour clocks and it is common for people to routinely switch between the two. Most English-speaking countries still prefer a 12-hour AM/PM clock. Despite the use in the military circle and for some governmental purposes, civilian life in the US is still set around a 12-hour clock. Other English-speaking countries like New Zealand and Australia use 12-hour clocks, though it is not uncommon to use a 24-hour time convention depending on the context. The English-speaking parts of Canada mostly use a 12-hour clock, while the French-speaking province of Quebec mostly opts for a 24-hour clock, like France.


In summary, the 24-hour clock, known as “military time” in the US, is a time keeping convention that assigns a number of 0-23 to each of the 24 hours of the day. Military time is often used instead of a 12-hour clock because it is an unambiguous way to report time that is needed in situations where temporal synchronization is of the utmost importance. Most non-English speaking countries in the world use some version of a 24-hour clock, while most English-speaking countries use a 24-hour clock for official and military purposes and a 12-hour AM/PM clock for civilian use.