Converting between Measurement Systems

Most prescriptions are written in SI, however, occasionally need may arise to convert a weight or a measurement from one units of system to units of another system. Table G provides commonly used equivalents for different measurement system.

Unit conversations needs to remember:

1. Kilograms to pounds
2. Centimeters to inches
3. Ounces to grams
4. Fluid ounces to milliliters (30 mL)
5. Tablespoons/teaspoons/mL

Table G: Metric and commonly used equivalents for various systems of measurement

Length Base unit is meter (m)	Weight Base unit is gram (g)	Volume Base unit is liter (l)
Symbol Equivalent 1 meter M 39.37 in 1 inch in 2.54 cm	Symbol Equivalent 1 gram G 15.432 grain (gr) 1 kilogram Kg 2.2 pound (lb) (avoirdupois) 1 grain Gr 64.8 milligram (mg); 65 mg is frequently used 1 ounce (avoir.) oz, ℥ 28.35 gram (g) 1 ounce (apoth.) = oz, ℥ 31.1 gram (g) 1 pound (avoir.) lb 454 gram (g) 1 pound (apoth.) lb 373 gram (g)	Symbol Equivalent 1 milliliter ♏ 16.23 minim 1 fluid ounce f℥ 29.57 ml 1 gallon Gal 3785 ml 1 pint Pt 473 ml

Solved Problem: If 3 ounces (apoth) of an ointment cost $6, calculate the cost of 40 g of ointment Approach: Convert the ounces into grams and then set up a proportion. $$ {31.1\ g \over 1\ oz} ={ x\ g \over 3\ oz} $$ $$ {3\ Oz} ={ 93.3\ g} $$ Set up a proportion to calculate the price of 40 g, $$ {$6 \over 93.3\ g} ={ $x\ \over 40} $$ Answer: $ 2.57

Solved Problem: Add together 1 gal, 1 qt, 1 pt, f℥ iii and express the total in ml. Approach: Convert all the measurement units to ml and then add. Answer: 5292.7 ml