Metric Units & Converting Between Them

What is the difference between metric and Imperial?

Imperial units were the standardization of the old English units in the British Empire. The Imperial system has loads of different units for different sizes of things, and they don't always play nicely with each other. Converting between different Imperial units can be complex, and requires that one memorize quite a few equivalences.

On the other hand, metric units are very nice to work with, since they are all multiples of ten (or a hundred, or one-tenth, etc) of each other. You can convert between the various different metric sizes by merely moving the decimal point the correct number of places in the correct direction.

Is the US metric or Imperial?

The United States uses the Imperial system. It is joined in this usage by Liberia (a West African country founded by African-Americans) and Myanmar.

Why does the US still use the Imperial system?

I dunno. We're lazy, and kinda stupid sometimes, and— I dunno! Shut up! *sniffles* *pouts*

We really have no good reason.

What are the basic units of measure in the metric system?

The basic metric units are meters (for length), grams (for mass or weight), and liters (for volume). And the different units convert into one another rather nicely, with one milliliter equalling one cubic centimeter (where one Cubic Centimeter is the "cc" of medical shows on television) and one gram being the mass (or weight) of one cc of water.

What are the commonly used metric prefixes?

There are many metric-unit prefixes, but the usual ones required in school are these: kilo-, hecto-, deka-, deci-, centi-, and milli-. To convert between the various prefixes, and thus the variously-sized units, you just move up and down this list of prefixes, moving the decimal point as you go.

How can I keep track of the order of the prefixes?

To remember the prefixes in order, you can use the following sentence:

King Henry Doesn't [Usually] Drink Chocolate Milk

The first letters of the words stand for the prefixes, with "Usually" in the middle standing for the "unit", being meters, grams, or liters. Many memory phrases omit the "Usually", and consequently students forget where the basic unit goes, messing up their conversions. Leave the "Usually" in there so you can keep things straight:

kilo- hecto- deka- [unit] deci- centi- milli-

Since each step is ten times or one-tenth as much as the step on either side, we have:

1 kilometer = 10 hectometers = 100 dekameters = [1000 meters] = 10 000 decimeters = 100 000 centimeters = 1 000 000 millimeters

Alternatively, we can go from the smallest prefix to the largest:

1 milliliter = 0.1 centiliters = 0.01 deciliters = [0.001 liters] = 0.000 1 dekaliters = 0.000 01 hectoliters = 0.000 001 kiloliters

The point here is that you move from one prefix to the next by moving the decimal point one place, and filling in, as necessary, with zeroes. To move to a smaller unit (that is, to move to a unit whose prefix is some number of places further to the right in the listing), you move the decimal place to the right that same number of places, and vice versa. Together with the prefix sentence ("King Henry..."), this makes conversion between the different metric sizes very simple.

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How do you know which way to move the decimal point when converting between metrix prefixes?

When you move from one sized prefix (say, centi-) to another sized prefix (say, kilo-), you'll be moving five spots to the left in the "King Henry Doesn't [Usually] Drink Chocolate Milk" sentence; move the decimal point five spots to the left, also.

Logically, when you're converting between the different sized prefixes, keep in mind that, if you're going to a bigger prefix, then you'll get a smaller number, so you should move the decimal point to the left. If you're moving to a smaller prefix, then you'll get a bigger number, so you should move the decimal point to the right.

What is an example of converting between differently prefixed metric values?

• Convert 12.54 kilometers to centimeters.

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• Convert 457 mL to hL.

What are the steps for converting between differently-sized metric units?

1. Memorize the correct order of the metric units.
2. Make sure to include the [units] notation in the right spot.
3. Count off the number of spots you move in going from the initial prefix to the ending prefix.
4. Note the direction in which you moved between the initial prefix and the ending prefix.
5. Move the decimal point in the starting number the same number of places as in Step 3, and in the same direction as in Step 4.
6. Fill in any empty spaces with zeroes, as needed.
7. Remember to put the correct prefix on the resulting number.

That's all there is to metric conversions. As long as you keep the prefixes straight and remember where in the sequence the "units" name goes, you'll be fine. Just count the number of jumps and note the direction; then move the decimal point the same direction and the same number of places.