Lesson 1: Convert Measurement Units

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Units of length:

A conversion factor is a fraction equal to 1, such as $\frac{3 \text{ feet}}{1 \text{ yard}}$. We choose the factor that cancels the old units and leaves the new ones. Such conversion factors are also called unit fractions.

Examples

• A person is 5 feet 4 inches tall. To express this in inches, calculate $5 \times 12 + 4 = 64$ inches.

• A piece of fabric is 90 inches long. To find its length in feet, you divide: $\frac{90}{12} = 7.5$ feet.

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Metric Units of Length:

The conversion factors in the metric system are all powers of 10.
This property makes the metric system easy to use, because we can convert between units simply by moving the decimal point.

Examples

• A table is 2.5 meters long. To convert this to centimeters, you move the decimal two places to the right: $2.5 \text{ m} = 250 \text{ cm}$.

• A small insect measures 6 millimeters long. In centimeters, this is $6 \div 10 = 0.6$ centimeters.