For most of human history, systems of weights and measurement have varied widely between lands, and there was rarely a simple conversion from one system to another. Systems of measurement often spread only by imperial conquest—from that spread, the standard system used by the British Empire (the Imperial system) became the most commonly used, but it was not alone.
During the scientific revolution, the need for a standardized system was recognized, and governments concurred that trade would be simplified with the same units of measurement used by all sides. The standardization of measurement was a long process, beginning in the late 18th century, but on May 20, 1875, the first Diplomatic Treaty of the Metre was signed by seventeen countries (including the United States, who maintains a good standing with the Metre Convention to this day, despite its attempt to metricate in the 1970s being a rather stunning failure), affirming the standard arbitrary measurements put forth by the document. Every year since the centennial of the Metre Convention, May 20 has been celebrated as International Metrology Day.
The international system of units (the metric system, or SI) is based off of six basic units—the second (time), metre (length), Kelvin (temperature), kilogram (mass), ampere (electric current), candela (luminous intensity), and the mole (amount of substance). All countries use the metric system to some significant degree, aside from the United States, Burma, and Liberia. However, that doesn’t mean that there aren’t other odd and arbitrary units of measurement out there. John Green covered 36 of these units on the recent mental_floss video.
The theme of this year’s Metrology Day celebrations is “Metrology in Daily Life,” and here are 12 measurements you probably don’t notice as you go about your day.
1. Your body only contains about 5.5 liters of blood, but your heart cycles over 7500 liters of blood (around 2000 U.S. gallons) through it each day. That’s enough to fill almost 48 oil barrels.
2. Humans shed around 500 million skin cells a day, adding up to 0.003 oz of skin each hour, 0.072 oz per day, and almost 26.3 oz of cells every year. It takes four to five large bananas to comprise the same weight.
3. The mucous membranes in your head produce between 1 and 1.5 liters of mucus a day. Thankfully, most of that drains directly down the back of your throat, unnoticed. When you’re sick, you generally don’t produce more of it, but it’s more noticeable because its consistency has changed.
4. Each day, the average adult—male or female—speaks about 16,000 words.
5. You probably lose around 100 hairs from your head every day, which can sound like a lot, but the average blonde has 150,000 hairs on their head. Brunettes, with brown or black hair, range around 100,000, and redheads, while last, still have over 80,000 hairs covering the scalp.
6. Each hair stays on your scalp for between 2 and 6 years, and is growing for all but approximately the last 3 months of its “lifespan.”
7. The average American eats around 2000 pounds (900 kg) of food per year (or almost 5.5 pounds (2.5 kg) of food per day). The 1968 VW Beetle weighed in similarly.
8. Helping to digest that food are between 600 and 5000 distinct species of bacteria living in the healthy human gut. All of those species add up to over 100 trillion bacterial cells in the body, outnumbering “human” cells 10-to-1. Don’t worry, you’re not completely bacteria. Those single-celled organisms generally weigh less than 5 pounds (2.3 kg).
9. The human skeleton makes up about 18 percent of our weight (around 32 pounds, or 15 kg in a 180 pound/81 kg person), and can support five times as much pressure as a steel bar with the same dimensions. Frequently-used bones (such as the femur in a runner, or the arm bones in a tennis player) can support up to 8 times as much pressure as a steel bar with the same dimensions.
10. Want to make those bones stronger? Brisk walking can significantly strengthen the lower limbs for those whose current activity level falls around the U.S. average—less than 6000 steps taken every day. While no industrialized country surpasses the ideal average of 10,000 steps per day, Australians come closest, with a 9965-step average in the sample group.
11. Working out works our sweat glands out, too! The human body sweats an average of 1.5 L/hour during physical exertion, but can sweat up to 3 L/hour if extremely taxed or in high temperatures at the same time. A sedentary person in a comfortable environment isn’t sweat-free, though—every day still brings about 1 L of sweat, with more than half a pint of it coming from the feet alone!
12. Humans blink around 10 to 15 times a minute, with each blink lasting around 100 milliseconds. This adds up to almost 16 minutes of the day spent blinking, assuming one sleeps 8 hours a night.