4.4: Metric Prefix Conversions
To express a quantity in a different metric prefix that what it was originally given, all we need to do is skip the decimal point to the right or to the left as needed. Notice that the metric prefix “number line” in the previous section was laid out from larger to smaller, left to right. This layout was purposely chosen to make it easier to remember which direction you need to skip the decimal point for any given conversion.
Example problem: express 0.000023 amps in terms of microamps.
0.000023 amps (has no prefix, just plain unit of amps)
From UNITS to micro on the number line is 6 places (powers of ten) to the right, so we need to skip the decimal point 6 places to the right:
0.000023 amps = 23. , or 23 microamps (µA)
Example problem: express 304,212 volts in terms of kilovolts.
304,212 volts (has no prefix, just plain unit of volts)
From the (none) place to kilo place on the number line is 3 places (powers of ten) to the left, so we need to skip the decimal point 3 places to the left:
304,212. = 304.212 kilovolts (kV)
Example problem: express 50.3 Mega-ohms in terms of milli-ohms.
50.3 M ohms (mega = 10 6 )
From mega to milli is 9 places (powers of ten) to the right (from 10 to the 6th power to 10 to the -3rd power), so we need to skip the decimal point 9 places to the right:
50.3 M ohms = 50,300,000,000 milli-ohms (mΩ)
Review
- Follow the metric prefix number line to know which direction you skip the decimal point for conversion purposes.
- A number with no decimal point shown has an implicit decimal point to the immediate right of the furthest right digit (i.e. for the number 436 the decimal point is to the right of the 6, as such: 436.)