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MonApr 7

Metric System Day – April 7, 2025

Metric System Day takes place on April 7 every year. Now often used as a synonym for the International System of Units (or S.I.), the metric system is a system of measurement used in most countries of the world except the United States and a few other countries. The metric system was introduced by France in 1799 and it’s an original, decimal-based (based on powers of 10) measurement format based on meters and kilograms. Base units in the metric system include kilograms, meters, and liters. The metric system also uses the Kelvin scale (or the Celsius scale) to measure the temperature. The decimal-based prefixes in the metric system include milli, centi, deci, and kilo. However, these prefixes are not used with the temperature degree.

History of Metric System Day

The history of the metric system goes all the way back to 1586 when Flemish mathematician Simon Stevin published a leaflet titled ‘De Thiende’ (‘The Tenth’). In the pamphlet, Stevin emphasized the importance of measuring in decimals and predicted that one day, the world would use decimals in standard measurement. Well, Stevin’s prophecies didn’t come true until over two centuries later when Napoleon became the emperor of France and in 1799 inaugurated the metric system. As Napoleon’s European conquest advanced, he also introduced the metric system to his new territories. However, as soon as he was defeated at the Battle of Waterloo in 1815, France and most of Napoleon’s former colonies returned to using their old systems of measurement. In 1837, France returned to the use of the metric system, and in 1840 — some 50 years after its inauguration — the system became compulsory throughout France.

Other countries such as the newly-formed Kingdom of the Netherlands formed in 1815 also adopted the use of the metric system in 1820 as a unified system of measurement. Similarly, the German Empire formed from the old German Confederation in 1871 continued to use the metric system. In the same year, the newly-amalgamated Italy also opted for the metric system in preference to the former systems of measurement. Between 1875 and 1914, other countries like Brazil, Spain, Portugal, Norway, Mexico, Argentina, Peru, Columbia, Sweden, Denmark, Finland, Paraguay, Philippines, and Vietnam also adopted the metric system. In 1866, the U.S. passed a law allowing Americans to use either the metric system or U.S. customary units for commercial purposes. Many years later — precisely in 1897, the United Kingdom also passed a similar law allowing its citizens to choose between the metric system or Imperial units for trade.

Metric System Day timeline

Simon Stevin’s Prophetic Pamphlet

Flemish mathematician Stevin emphasizes the importance of measuring in decimals in his pamphlet ‘De Thiende.’

Napoleon Metricates France

Emperor Napoleon inaugurates the use of the metric system in France.

Introducing the S.I.

The International Institute of Metrology (B.I.P.M.) publishes the International System of Units (or S.I.).

A Congress Act for the Metric System

U.S. Congress passes the Metric Conversion Act designating the metric system as the preferred system of weights and measures.

Metric System Day FAQs

Is day a metric unit?

The second is the base unit of time in the modern S.I. system. It forms multiples and submultiples with decimal (metric) prefixes such as kiloseconds, milliseconds, and nanoseconds. While S.I. accepts other units of time like a minute, hour, and day, these units are not part of its units.

What is the metric system based on?

The metric system is based on the meter for length and the kilogram for mass.

What three things are the metric system based on?

The metric system is a standard system of measurement that uses the meter, liter, and gram as base units of length (distance), capacity (volume), and weight (mass) respectively.

Metric System Day Activities

  1. Learn more

    You can spend the Metric System Day reading and learning more about the metric system, its specific units, and what each unit means. Read more about the origin of the metric system, its pioneers, and its evolution.

  2. Advocate for its wider adoption

    This holiday is also useful to express the necessity of widely adopting the metric system in the U.S. It will definitely make measurements easier and unified.

  3. Share the news

    Share your thoughts and perspectives about Metric System Day on social media with the hashtag #MetricSystemDay. You can also use your social media presence to discuss the history and benefits of the metric system.

5 Interesting Facts About The Metric System

  1. There was a metric calendar

    Launched in 1795, the Metric Calendar (also called the French Republican Calendar) divided the year into 12 months, each month divided into three 10-day weeks.

  2. There was a metric clock, too

    Each day was broken down into 10 decimal hours, and each hour was 100 decimal minutes.

  3. The U.S. is not the only resistor

    The U.S., Liberia, and Myanmar remain the antagonists against the metric system.

  4. Thomas Jefferson was a vocal advocate

    Jefferson, Lord Kelvin, and Alexander Graham Bell were all passionate supporters of the metric system.

  5. America pioneered its use for currency

    Through the Mint Act of 1792, the U.S. became the first English — speaking country to create a decimal-based currency.

Why We Love Metric System Day

  1. Its history and evolution

    After its adoption in 1799, the metric system endured some resistance and changes. Even France, its pioneer nation, once ditched its use early in the post-Napoleonic era.

  2. Acknowledging its advocates

    Thanks to the scientists who revolutionized its adoption in 1850, the metric system would’ve been long forgotten. On this day, we celebrate the global adoption of the metric system and the dogged minds who worked to standardize the system.

  3. Remembering metrication laws

    On this day, we also remember the laws, organizations, and treaties (such as the Treaty of the Meter) that industrialized countries like the U.S. created for the adoption of the metric system. Such treaties created the International Bureau of Weights and Measures, now called the SI.

Metric System Day dates

2025April 7Monday
2026April 7Tuesday
2027April 7Wednesday
2028April 7Friday
2029April 7Saturday

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