NURS 1510
Metric: decimal system, most logically
organized.
Each unit is organized into units of 10. In X
the decimal moves to the “R”; in division it
moves “L”
Basic measurement=meter(L), liter(volume),
gram(weight)
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Basic units:
◦ Deci 1/10 or 0.1
◦ Centi 1/100 or 0.01
◦ Milli
1/1000 or 0.001
 500mg or 0.5g, not 1/2g
 10ml or 0.01L, not 1/100L
◦ With fractions the zero is always place in front of
the decimal to prevent error
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In metric system, division or multiplication
are used, ie, to change mg to g. divide by
1000 or move the decimal 3 points to the left
To convert liters to ml, multiply by 1000 or
move the decimal 3 points to the right
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To convert units of measurement within the
apothecary or household system, must know
the equivalent.
Example: To convert ounces to quarts must
know 32 oz is = to 1 quart
To convert 8 oz to a quart measurement,
divide 8 by 32 to get the equivalent, ¼ or
0.25 quart
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When looking at a medication order, ask
yourself 3 questions:
What did the MD order? (desired quantity)
What do I have on hand? (dose available)
What conversion factor (conversion
do I need?
factor)
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The desired quantity is the MD order, (10mg,
v gr)
The dose available is found on the drug label,
(tablet, number of capsules, ml)
*Remember, the quantity of tablets, capsules,
or ml is always the numerator of the dose
available; the amount (or dosage) is in the
denominator
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To decide which equivalent measure should
be in the numerator and which should be in
the denominator, look at the units of measure
in the desired quantity.
The units of measure in the desired quantity
should be in the denominator of the
conversion factor (i.e.,if the desired quantity
is 100 mg and the equivalent conversion
factor is 1000 mg = 1 g, then the conversion
factor in fraction form should be 1 g /
1000mg
Desired quantity x Dose available X Conversion
(if factor needed) = Amount to Administer
This is a simple formula that uses ratio and
proportions which will help you both correctly
set up and solve dosage calculation problems
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MD order: ASA 300 mg q4h prn pain
Drug label: ASA 1 tab = v gr
Conversion factor: 1 gr = 60 mg
5gr x 1 tab x 60 mg = x
300mg
1 gr
5 x 1 tab x 60 = 300 tab = x
300
300
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300 tab = x
300
x = 1 tab
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Another basic formula that can be used when
preparing solid or liquid forms:
Desire dose X Amt on hand = Amt to give
dose Have
Demerol 50 mg ordered comes in 100 mg vial
in I cc
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Amount in cc’s X drip factor = gtt/min
time in minutes
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1 gram (G) = 1000 milligrams (mg)
1000 micrograms (mcg) = 1 mg
60-65 mg = 1 grain (gr)
1 fluid ounce = 30 ml or 2 tablespoons
1 teaspoon = 5 ml
1000 ml = 1 quart or 1 liter
1 kg = 2.2 pounds (lb)
1 inch = 2.54 cm