Important Pharmacy Conversions
Volume Conversions
| 1mL | 20 drops |
| 1 teaspoon | 5mL |
| 1 tablespoon | 15mL |
| 1 fluid ounce | 30mL |
| 1 pint | 480mL |
Weight Conversions
| 1 ounce | 28-30 grams |
| 1 kilogram | 2.2 pounds |
| 1 grain | 65mg |
| 1 pound | 454 grams |
| 1 gram | 1000mg *more about this in the section about metric-to-metric conversions |
Conversion Between Metric Units
The other important conversion set needed in the pharmacy is between metric units. Metric conversions are significantly easier than those between metric and standard or apothecary measurments, which will be talked about more in a moment.
There are two basic ways to do conversions within the metric system. First, you can multiply the number by the required 10^x. For example. Grams to milligrams, you multiply by 10^3 (1000). To go from milligrams to kilograms, you multiply by 10^6. Therefore, 3.5g is 3500mg. As you can see, this is pretty difficult if you're not already fairly familiar with the metric system.
The following chart is useful for conversion of units. The smaller prefixes are significantly less commonly used in day-to-day life... let alone in the pharmacy. The units you will encounter most often are kilo-, milli-, and micro-... as well as your base units of grams or liters (or outside of the pharmacy in meters). So let's continue using our example of 3.5g. (There's more explanation below the chart, too.
| kilo- | hecta- | deca- | _____ | deci- | centi- | milli- | --X-- | --X-- | micro- |
| kilo- | hecta- | deca- | 3. | 5 | centi- | milli- | --X-- | --X-- | micro- |
As you can see, the decimal goes in the space directly after the desired prefix, in this case, none and the numbers go into the columns. To convert the number to milligrams, move the decimal to the space directly after milligrams....
| kilo- | hecta- | deca- | _____ | deci- | centi- | milli- | --X-- | --X-- | micro- |
| kilo- | hecta- | deca- | 3 | 5 | . | --X-- | --X-- | micro- |
Then you fill the zeroes in up to the decimal point and:
| kilo- | hecta- | deca- | _____ | deci- | centi- | milli- | --X-- | --X-- | micro- |
| kilo- | hecta- | deca- | 3 | 5 | 0 | 0. | --X-- | --X-- | micro- |
Viola! 3500mg. This works the other way, too by placing the final zero before the decimal point:
| kilo- | hecta- | deca- | _____ | deci- | centi- | milli- | --X-- | --X-- | micro- |
| 0. | 0 | 0 | 3 | 5 | centi- | milli- | --X-- | --X-- | micro- |
So 3.5g is 0.0035 kilograms. I've found this significantly easier than trying to remember which power of ten I need to multiply or divide by.
Apothecary and Household Measurements
Of course, as mentioned above, there are more esoteric conversion factors. While these do not come up often, you should still be aware of them. The apothecary system used to be the pharmacy standard, but was abandoned (I think you'll see why). The household measurements are what most people think of when confronted with a recipe.
| 1mL | 15 minims |
| 1 fluid dram | 4mL |
| 1 ounce | 8 drams |
| 1 dram | 60 grains |
Household Conversions
| 1 cup | 8 ounces |
| 1 pint | 2 cups |
| 1 quart | 2 pints |
| 1 gallon | 4 quarts |
Apothecary Conversions
The easiest way to learn things like this by memorization is throuh the use of notecards.
Happy studying!
C. Samuels
In real life? Hardly any conversion is done except mL to teaspoon or vice versa. Quite a bit of that is just memorization too, not even actually doing the math. Everything else is just very simple math like calculating days supply or quantities (i.e. memorizing that a box of albuterol neb sol has 25 vials of 3ml each so the system needs a qty of 75 to be input for 1 box to be dispensed. So if a script writes for 2 boxes you'd just need to know to do 75x2 and put 150 for the qty).I also have many suggestions about the conversion through this Conversion Calculator.
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