Our existing system has units of measure related by various numbers that can be difficult to multiply and divide, but in the metric system units are related by powers of ten, making the math much simpler. Here is a comparison of how units are related in both systems.

WEIGHT | ||||||
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U.S. SYSTEM (Avoidupois) |
METRIC SYSTEM |
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Unit | Abbreviation | Equivalents | Unit | Abbreviation | Equivalents | |

Ounce | oz. | 0.0625 pound | Microgram | µg or mcg | 0.000001 gram | |

Pound | lb. or # | 16 oz. | Milligram | mg | 0.001 gram | |

Short ton | 2000 lbs. | Gram | g | |||

Long ton | 2200 lbs. | Kilogram | kg | 1,000 grams | ||

Metric ton | t | 1,000,000 grams, 1,000 kilograms |

LIQUID MEASURE | ||||||
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U.S. LIQUID MEASURE |
METRIC SYSTEM |
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Unit | Abbreviation | Equivalents | Unit | Abbreviation | Equivalents | |

Teaspoon | tsp. | 1/6 oz. | Microliter | µl | 0.000001 liter | |

Tablespoon | Tbsp. | 3 tsp., 1/2 oz. | Milliliter | ml | 0.001 liter | |

Fluid ounce | fl. oz. | 2 Tbsp. | Centiliter | cl | 0.01 liter | |

Cup | 8 oz. | Liter | l | |||

Pint | pt. | 2 cups | Hectoliter | hl | 100 liters | |

Quart | qt. | 2 pints | Kiloliter | kl | 1,000 liters | |

Gallon | gal. | 4 quarts |

LENGTH |
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U.S. SYSTEM |
METRIC SYSTEM |
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Unit | Abbreviation | Equivalents | Unit | Abbreviation | Equivalents | |

Inch | in. or " | 0.083 foot | Micrometer | µm | 0.000001 meter | |

Foot | ft. or ' | 12 inches | Millimeter | mm | 0.001 meter | |

Yard | yd. | 3 feet, 36 inches | Centimeter | cm | 0.01 meter | |

Rod | rd. | 5.50 yards, 16.5 feet | Meter | m | ||

Mile | mi. | 5280 feet, 1760 yards, 320 rods | Kilometer | km | 1,000 meters |

AREA | ||||||
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U.S. SYSTEM |
METRIC SYSTEM |
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Unit | Abbreviation | Equivalents | Unit | Abbreviation | Equivalents | |

Square inch | sq. in. or in^{2} | 0.0069 square foot | Square centimeter | sq cm or cm^{2} | 0.0001 square meter | |

Square foot | sq. ft. or ft^{2} | 144 square inches | Are | a | 100 square meters | |

Square yard | sq. yd, or yd^{2} | 9 square feet, 1296 square inches | Hectare | ha | 10,000 square meters | |

Square rod | sq. rd. or rd^{2} | 30.25 square yards, 0.00625 acre | Square kilometer | sq km or km^{2} | 1,000,000 square meters | |

Acre | ac. | 4840 square yards, 43,560 square feet | ||||

Square mile | sq. mi. or mi^{2} | 640 acres, 102,400 square rods |

VOLUME | ||||||
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U.S. SYSTEM |
METRIC SYSTEM |
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Unit | Abbreviation | Equivalents | Unit | Abbreviation | Equivalents | |

Cubic inch | cu. in. or in^{3} | 0.00058 cubic foot | Cubic centimeter | cu cm or cm^{3} or cc | 0.000001 cubic meter | |

Cubic foot | cu. ft. or ft^{3} | 1728 cubic inches | Cubic decimeter | dm^{3} | 0.001 cubic meter | |

Cubic yard | cu. yd. or yd^{3} | 27 cubic feet, 46,656 cubic inches | Cubic meter | m^{3} | ||

Cubic mile | cu. mi. or mi^{3} | 5,451,776,000 cubic yards, 147,197,952,000 cubic feet | Cubic kilometer | km^{3} | 1,000,000,000 cubic meters |

A System in the Metric System

Start with a basic unit for each category of measurement, as follows: the meter for length, the gram for weight, and the liter for capacity.

Then have a standard set of prefixes to define the fraction or multiple of the basic unit, as follows:

micro = 0.000001 = one millionth

milli = 0.001 = one thousandth

centi = 0.01 = one hundredth

deci = 0.1 = one tenth

deka = 10 = ten

hecto = 100 = one hundred

kilo = 1,000 = one thousand

mega = 1,000,000 = one million

So, for example, one microgram is a millionth of a gram and one kilometer is one thousand meters. But some of the prefixes are not used with some of the units, some are rarely used, and there are a few units that don’t follow this pattern, such as the metric ton instead of megaton for one million grams, and the hectare for 10,000 square meters.

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