Basic Math and PreAlgebra
APPENDIX E. Measurement
Throughout this book, you’ve encountered units of measurement from both the customary and the metric system. This appendix covers the key information you need to function in each system and just a word or two about shifting from one to the other. In each system, you measure three basic quantities: length (or distance), mass (which, with gravity, determines weight), and volume.
Metric System
The metric system of measurement (also called the International System of Units) is used around the world, and its popularity likely stems not just from the idea of a universal system but from the consistent decimal logic of the system. Everything is based on tens. There are base units of length, mass, and capacity. The larger and smaller units are created by dividing a base unit by 10 or 100 or 1,000 (and so on) or by multiplying by 10 or 100 or 1,000 (and so on).

Basic Unit 
Approximation 
Official Definition 
Length: 
meter 
The distance from a doorknob to the floor 
The path length travelled by light in a given time 
Mass: 
gram* 
The mass of a paperclip 
The mass of one cubic centimeter of water at 4°C 
Capacity: 
liter 
The volume of a mediumsized bottle of soda or water 
The capacity of a container with a volume of 1,000 cubic centimeters 
*The current standard defines the kilogram as the base unit and the gram as one onethousandth of a kilogram, but the system is easier to understand if you begin with gram, the original base unit.
Notice that the units of length, mass, and capacity are linked. The liter is the capacity of a cube 10 centimeters wide by 10 centimeters long by 10 centimeters high, connecting length and volume to capacity. The gram is the mass of a cubic centimeter of water, which associates mass with volume and length and capacity.
From the basic units, you can break into smaller units or build into larger units, always multiplying or dividing by powers of ten. The naming of those units follows the same system of prefixes whether the base unit is meter, liter, or gram. Here are the prefixes and some ideas to help you imagine some of the commonly used units.
Smaller 

1/1,000 
milli 
Millimeter: approximately the thickness of 10 sheets of paper Milligram: the mass of a grain of salt Milliliter: about 20 drops of water 
1/100 
centi 
Centimeter: approximately the diameter of a pencil eraser, or the diameter of a AAA battery Centigram: the approximate mass of a U.S. dollar bill, or about two raisins. Centiliter: about half a teaspoon 
1/10 
deci 
Decimeter: approximately the length of a crayon Decigram: two nickels Deciliter: about onefourth of a can of soda 
Larger 

10 
deca (or deka) 
Decameter: a long bus or train car Decagram: about half the mass of a small mouse Decaliter: approximately the capacity of a teapot 
100 
hecto 
Hectometer: about a city block Hectogram: the mass of an orange Hectoliter: about the capacity of a small refrigerator 
1,000 
kilo 
Kilometer: about 2.5 laps on a stadium track Kilogram: mass of a dictionary or large textbook Kiloliter: the capacity of about eight large trash cans 
When you’re changing units within a system, the thing to remember is balance. If you’re changing to a unit of a smaller size, you’ll have more of them. If your new unit is bigger, you’ll have fewer. And always, it’s about 10. Multiply by 10 if you’re going to a smaller unit, and divide by 10 to get to a bigger unit.



Base 



1,000 millimeters 
100 centimeters 
10 decimeters 
1 meter 
0.1 decameter 
0.01 hectometer 
0.001 kilometer 
1,000 milligrams 
100 centigrams 
10 decigrams 
1 gram 
0.1 decagram 
0.01 hectogram 
0.001 kilogram 
1,000 milliliters 
100 centiliters 
10 deciliters 
1 liter 
0.1 decaliter 
0.01 hectoliter 
0.001 kiloliter 
Customary System
What’s commonly called the customary system is a system that developed over time and remains popular in the U.S. and a few other spots around the world. It is very similar to the British imperial system, as both were derived from English units. The customary system was not designed as a unified system, so there are many different rules to remember.
Length
In the customary system, length is measured in units like inches, feet, yards, and miles.
Unit 
Approximation 
Conversion 
Inch 
From the knuckle to the tip of your thumb 

Foot 
The length of a large man’s foot 
12 inches = 1 foot 
Yard 
The height of the kitchen counter 
3 feet = 1 yard 
Mile 
A 20minute walk 
5,280 feet = 1,760 yards = 1 mile 
Mass (Weight)
The customary system measures mass (but often calls it weight) in ounces, pounds, and, for really heavy things, tons.
Unit 
Approximation 
Conversion 
Ounce 
Ten pennies 

Pound 
A package of butter or bacon, or a football 
16 ounces = 1 pound 
Ton 
A car 
2,000 pounds = 1 ton 
Capacity
The customary system uses ounce to measure capacity, but an ounce measured by capacity is not necessarily equivalent to an ounce of mass. If you have an ounce of something (capacity), whether it weighs an ounce or not depends on what it is.
Unit 
Approximation 
Conversion 
Ounce 
A little container of coffee cream 

Cup 
A container of coffee 
8 ounces = 1 cup 
Pint 
A small container of ice cream 
2 cups = 1 pint 
Quart 
A container of milk 
2 pints = 1 quart 
Gallon 
A large can of paint 
4 quarts = 1 gallon 
Conversion
Although you may not often need to convert from one system of measurement to another, when you are, you may not have the tools or formulas handy to make an exact conversion. Here are some rules of thumb that can help you make an approximate conversion.
• An inch is about 2.5 centimeters.
• A meter is a little more than a yard. A meter is about 39 inches and a yard is 36 inches.
• A mile is about 1.6 kilometers.
• A liter is a little more than a quart.
• A kilogram is about 2.2 pounds.
WORLDLY WISDOM
A famous number sequence, called the Fibonacci sequence, is easy to recreate and can be used for quick, approximate conversions of length and distance. The Fibonacci sequence begins with two ones, then forms each of the next terms by adding the two previous terms.
1, 1, 1 + 1
1, 1, 2, 1 + 2
1, 1, 2, 3, 2 + 3
1, 1, 2, 3, 5, 8, 13, 21,...
Two adjacent terms of the Fibonacci sequence can give you a rough conversion of miles and kilometers. For example, 5 kilometers is approximately 3 miles, (3.10686 miles) and 8 kilometers is approximately 5 miles (4.97097).