Lesson 2: Converting Between SI Units - Conversion Ratios

   Constructing Knowledge

Conversion ratios can be used to represent a given measurement in a different unit. The relationship between two units can be expressed as a conversion ratio, or fraction, that is equal to one.

Conversion Ratio
A ratio, equal to 1, that can be used to convert between different units.

Conversion Ratios
Written as an equality Written as a fraction equal to 1
100 cm = 1 m \(\frac{100\,\text{cm}}{1\,\text{m}}=1\)
1 km = 1000 m \(\frac{1\,\text{km}}{1000\,\text{m}}=1\)

Using the SI Prefix table (found in the section titled, 'The SI System Units'), you can always set up a ratio equaling one by pairing any two values in the Conversion Factor column because each value in that column is equivalent to 1 base unit.

For example, 100 cL = 0.1 daL because both are equivalent to 1 L.

100 cL = 0.1 daL can be rewritten as \(\frac{100\,\text{cL}}{0.1\,\text{daL}}\) = 1.

Notice that because conversion ratios always equal one, the numerator and denominator can be switched, as your needs require. This means that 100 cL = 0.1 dL can be written as \(\frac{100\,\text{cL}}{0.1\,\text{daL}}\) = 1 or as \(\frac{0.1\,\text{daL}}{100\,\text{cL}}\) = 1.

   Multimedia

A video demonstration of conversion ratios is provided.




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