How to Estimate Metric Amounts
One reason people sometimes feel uncomfortable using the metric system is that when you’re not familiar with it, estimating amounts in practical terms is hard. For example, if your friend invites you to a beach that’s 1/4 mile away, you prepare yourself for a short walk. And if they tell you that it’s 10 miles away, you head for the car. But what do you do with the information that the beach is 3 kilometers away?
Similarly, if someone tells you that the temperature is 85 degrees Fahrenheit, you’ll probably wear a bathing suit or shorts. And if they tell you it’s 40 degrees Fahrenheit, you’ll probably wear a coat. But what do you wear if they tell you that the temperature is 25 degrees Celsius?
Here you will learn a few rules of thumb to estimate metric amounts. In each case, you will see how a common metric unit compares with an English unit that you already feel comfortable with.
Estimate distances and speed
Here’s how to convert meters to feet: 1 meter is approximately 3.26 feet. But for estimating, use the simple rule that 1 meter is about 1 yard (that is, about 3 feet).
By this estimate, a 6-foot man stands about 2 meters tall. A 15-foot room is 5 meters wide. And a football field that’s 100 yards long is about 100 meters long. Similarly, a river with a depth of 4 meters is about 12 feet deep. A mountain that’s 3,000 meters tall is about 9,000 feet. And a child who is only half a meter tall is about a foot and a half.
Here’s how to convert kilometers to miles: 1 kilometer is approximately equal to 0.62 miles. For a ballpark estimate, you can remember that 1 kilometer is about 1/2 mile. By the same token, 1 kilometer per hour is about 1/2 mile per hour.
This guideline tells you that if you live 2 miles from the nearest supermarket, then you live about 4 kilometers from there. A marathon of 26 miles is about 52 kilometers. And if you run on a treadmill at 6 miles per hour, then you can run at about 12 kilometers per hour. By the same token, a 10 kilometer race is about 5 miles. If the Tour de France is about 4,000 kilometers, then it’s about 2,000 miles. And if light travels about 300,000 kilometers per second, then it travels about 150,000 miles per second.
Here’s how to convert liters to gallons: 1 liter is approximately equal to 0.26 gallons. A good estimate here is that 1 liter is about 1 quart (that is, there are about 4 liters to the gallon).
Using this estimate, a gallon of milk is 4 quarts, so it’s about 4 liters. If you put 10 gallons of gasoline in your tank, this is about 40 liters. In the other direction, if you buy a 2-liter bottle of cola, you have about 2 quarts. If you buy an aquarium with a 100-liter capacity, it holds about 25 gallons of water. And if a pool holds 8,000 liters of water, it holds about 2,000 gallons.
Here’s how to convert kilograms to pounds: 1 kilogram is approximately equal to 2.20 pounds. For estimating, figure that 1 kilogram is equal to about 2 pounds.
By this estimate, a 5-kilogram bag of potatoes weighs about 10 pounds. If you can bench press 70 kilograms, then you can bench press about 140 pounds. And because a liter of water weighs exactly 1 kilogram, you know that a quart of water weighs about 2 pounds. Similarly, if a baby weighs 8 pounds at birth, he or she weighs about 4 kilograms. If you weigh 150 pounds, then you weigh about 75 kilograms. And if your New Year’s resolution is to lose 20 pounds, then you want to lose about 10 kilograms.
The most common reason for estimating temperature in Celsius is in connection with the weather. The formula for converting from Celsius to Fahrenheit is kind of messy:
Instead, use the below handy chart to compare Celsius and Fahrenheit temperatures:
Any temperature below 0°C is cold, and any temperature over 30°C is hot. Most of the time, the temperature falls in this middling range. So now you know that when the temperature is 6°C, you want to wear a coat. When it’s 14°C, you may want a sweater or at least long sleeves. And when it’s 25°C, head for the beach!