How to Understand the Metric System

Learning Basic Metric Principles

Memorize the base units. Unlike the Imperial system, which uses many different units for the same quantity, the metric system uses a single base unit for each type of measurement. Each base unit is unique to that particular type of measurement. The base unit for measuring volume is the liter (L). The base unit for measuring length or distance is the meter (m). Due to a historic quirk, the base unit for mass actually is the kilogram, making it the only base unit that has a prefix. However, you still form larger and smaller units using prefixes in reference to a gram.

Use base units to form larger and smaller units. The base unit tells you what kind of measure you're making. The prefix before the base unit tells you the size of the measurement in relation to the base unit itself. The basic prefixes you'll encounter most often are kilo-, hecta-, deka-, deci-, centi-, and milli-. Kilo-, hecta-, deka-, and deci- all describe units larger than the base unit. Deci-, centi-, and milli- are used for units that are fractions of the base unit. Each prefix represents one decimal place. If you're familiar with computer memory measurements, such as megabytes and gigabytes, you're already familiar with the metric system prefixes. In computer memory, the "byte" is the basic unit. A megabyte is one million bytes, just as a mega-liter is one million liters.

Draw a diagram to help you remember order. If you're having trouble remembering which prefixes are larger than others, a diagram can help you recognize them and understand the relationships between them. It can also be helpful when you start converting between larger and smaller units. One easy type of diagram is a ladder. You can draw this vertically or horizontally, whichever works best for you. Draw seven rungs of the ladder, and place each of the prefixes above one rung. The largest, kilo-, will go on the top rung (farthest to the left, if you're drawing your diagram horizontally), down to the smallest at the bottom (or far right). The base unit is at the center of your diagram. The prefixes above, or to the left, of the base unit are a magnitude larger than the base unit. The prefixes below, or to the right, of the base unit are a magnitude smaller than the base unit. The degree of magnitude is determined by counting the number of rungs away from the base unit.

Try a mnemonic device to memorize the order of prefixes. A diagram may not work well for you if you aren't a visual learner, but you might find that a mnemonic device helps you remember the order of the prefixes. One mnemonic device for the order of prefixes in the metric system is "King Henry Died Ugly Drinking Chocolate Milk." The first letter of each word corresponds to the first letter of the prefix, with U standing in for the base unit. Don't think you have to use a mnemonic device someone else made up, though. If you make up your own it might be easier to remember. You also might want to try a mnemonic device if you're having trouble remembering the base unit. For example, try "My Large Giraffe" to remember that the base units for measuring length, volume, and mass are the meter, liter, and gram.

Relate metric units to each other. Metric units are ordered in magnitudes of ten, so each step up or down in size corresponds to one decimal place. Once you understand the base unit, you can build on it to create larger and smaller units by moving the decimal point to the left or the right. For example, suppose you have a measurement of 6500[.] meters, and you want to convert it into kilometers. The kilo- is three prefixes before the base unit, so you would move the decimal three places to the left. 6500 meters = 6.5 kilometers. Move the decimal to the left if you're converting smaller units into larger ones. Move it to the right if you're converting larger units into smaller ones. Add zeros if necessary to fill in the spaces. For example, 5 kilograms = 5,000 grams. The decimal was originally behind the "5," then you moved it three spaces to the right. Different base units also are related to each other. For example, one liter is equal to one kilogram. Be careful here – while the kilogram is considered the base unit to express mass in certain contexts, such as the mass or weight of a human being, the gram is still considered the base unit for mass or weight.

Thinking Metrically

Avoid converting between metric and non-metric units. If you want to truly understand the metric system, think of metric measurements as existing in your brain alongside Imperial measurements as two independent things. Think of the metric system as another language. If you learn a second language, you can learn by translating words and phrases from the second language into your first language, but to really understand the second language you have to learn to think in that language also. Instead of viewing metric measures as a "translation" of Imperial measurements, think about how you originally learned Imperial measurements. You know how much a gallon is because you've seen gallon jugs of milk all your life. You can start thinking metrically the same way.

Identify reference objects. You probably got a basic idea of different weights and measures using the Imperial system by equating them to the size of things you saw every day. You can use the same principles to better understand the metric system. For example, a doorknob on a door is typically about a meter up from the floor. An egg weighs about 50 grams. For volume, think about the size of a liter bottle of soft drink.

Label items around your house. To reinforce thinking in terms of meters instead of Imperial measurements, measure the size or weight of different items around your house. Start with items that you look at or use on a regular basis. You can use sticky notes to put the measurement on the object in a place where you can see it whenever you glance over at the object. Over time, you'll come to associate that object with that measurement in your head. For example, suppose you have a cookie jar that is 40 centimeters tall. You label the cookie jar with the measurement. If someone mentions something being 50 centimeters long, you might have a good idea of how long that thing is because you can add another 10 centimeters to the image of the cookie jar in your head.

Find metric measures for familiar distances. Especially if you travel internationally, you'll need to understand kilometers and meters so you can find your way around. Start by learning distances to places you frequent. If you commute to work or school every day, find out how many kilometers that location is from your house. For example, maybe you work at a store 12 kilometers from your house. If you're traveling overseas and you're told your hotel is 10 kilometers from the airport, you can compare that distance to the distance between your home and your job to decide whether you can walk that distance or need to call a cab.

Use metric measurements in the kitchen. The kitchen can be one of the easiest places to start incorporating the metric system into your everyday life, especially if you do a lot of cooking. Most cookbooks include both Imperial and metric measurements for ingredients. If alternate measurements are included in a recipe, you may want to strike them out with a black pen or marker so you won't be tempted to look at them. Replace all your measuring cups and spoons with their metric equivalents. When you cook, use those measures exclusively – try not to think about what that amount would be under the Imperial measurement system.

Focus on metric measurements at the grocery store. The grocery store is another place where it's easy to work on thinking metrically, because most food packages include metric and Imperial measurements on the label. Train yourself to automatically look at the metric measurement, and think about the amount of food in terms of the metric measurement rather than any other.

Converting Metric Values

Think in tens. The metric system simplifies units of measurement by converting between larger and smaller units using multiples of ten. Each larger unit is exactly 10 times larger than the previous unit. This can be difficult to get used to, since the Imperial measurement system is not set up this way. For example, there are 12 inches in a foot. To convert feet to inches, you must multiply by 12. However, since the metric system is arranged in multiples of ten, there's no complex math involved in converting metric measurements.

Learn the order of the prefixes. To create a metric unit, you add a prefix to the basic unit. These prefixes are ordered from largest to smallest: kilo-, hecta-, deka-, (basic unit), deci-, centi-, milli-. Each prefix corresponds to one multiple of 10. You can multiply or divide by a power of ten to move between larger and smaller units.

Divide to convert smaller units to larger units. If you have an unwieldy amount of smaller units, you can divide the large number by a magnitude of 10 and express the amount using larger units. This makes your figures cleaner and simpler. For example, suppose you have a bottle of juice that contains 2,000 milliliters. It would be a lot simpler and easier to understand if you said the bottle contained 2 liters of juice. You're probably familiar with the size of a 2-liter bottle. To convert 2,000 milliliters to liters, divide 2,000 by 10 three times, since milli- is three places from the base unit. 2,000 ÷ 10 ÷ 10 ÷ 10 = 2. When going from a unit larger than the base unit to one smaller than the base unit, simply count the number of steps between the two units. Each step is another multiple of 10.

Multiply to convert larger units to smaller units. Since there are tens more of a smaller unit than there are of a larger unit, you need to multiply by a magnitude of 10 to express a larger unit as a smaller unit. If you're comparing the size of two things, you typically want to compare using the same unit of measurement. This may require you to convert a larger unit down to a smaller unit in some contexts. For example, suppose you are making a list of restaurants within 1 kilometer of your house. The farthest restaurant is 1 kilometer away, but all the other restaurants are a number of meters away. Convert the distance of the farthest restaurant to meters by multiplying 1 by 10 three times, since kilo- is three steps away from the base unit, meter. 1 x 10 x 10 x 10 = 1,000 meters.