In nursing, there are currently three systems of measurement for drug dosage calculations:
 

METRIC	APOTHECARY	HOUSEHOLD
mcg -- microgram	m -- minim	tsp -- teaspoon
mg -- milligram	gr -- grain	T. or Tbs. -- tablespoon
Gm -- Gram	dr -- dram	c -- cup
kg -- kilogram	lb -- pound	pt -- pint
ml -- milliliter		qt -- quart
cc -- cubic centimeter

 

It will be easier to calculate if the conversion is made from the apothecary or household measurements to the metric system. It alleviates fractions.

Conversions to memorize:
 

METRIC/METRIC	HOUSEHOLD/HOUSEHOLD	BETWEEN SYSTEMS
1000 Gm = 1 kGm	1 Tbs. = 3 tsp	1 gr. = 60 mg (less than 1 gr.)
1000 L = 1kL	1 oz. = 2 Tsp.	15 gr. = 1000 mg (more than 1gr.
1,000 mL = 1 L	1000 cc = 1 qt.	2.2 lbs. = 1 kg
1,000,000 mcL = 1 L		1 ml = 1 cc
		1 tsp = 5 cc
		1 dram = 4 or 5 cc
		8 dram = 1 oz
		500 ml = 1 pt
		1000 cc = 1 qt (1 L)
		gr. 1/8 = 8 mg
		gr. 1/6 = 10 mg
		gr. 1/4 = 15 mg
		gr 1/2= 30 mg
		gr. 3/4 = 45mg
		gr. 1 = 60 mg
		gr. iss = 100 mg
		gr. V = 300 mg
		gr. VIIss = 500 mg
		gr. X = 600 mg
		gr. XV = 1000mg