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Metric System, Household Systems, Converting Within & Between
Systems
Calhoun Community College
A physician writes a prescription for Colchicine and accidentally orders “10.0 mg,” when he should have ordered “1.0 mg.”
That’s a tiny decimal error, a mistake even the best doctor could make.
But it can be catastrophic for the patient.
The higher dose could cause Colchicine poisoning, similar to arsenic poisoning: burning in the mouth and throat, excruciating abdominal pain. Internal organs would melt away and death would likely occur
within 24 to 72 hours.
The Shocking Truth About Medication Errors (http://www.forbes.com/sites/leahbinder/2013/09/03/the-shocking-truth-about-medication-errors/)
Preferred for prescribing and administering medication
It is a decimal system based on multiples of 10
Primary units of measurement is:
Gram for weight
Liter for volume
Meter for length
unit base the times1000or thousandone
unit base theof10
1or 0.1or tenth one
unit base theof 100
1or 0.01or hundredth one
unit base theof 1000
1or 0.001or h thousandtone
unit base theof 1,000,000
1or 0.000001or millionth one
kilo
deci
centi
milli
micro
© 2004 Delmar Learning, a division of Thomson Learning, Inc.
ALL RIGHTS RESERVED.
Weight g = gram (base unit)mg = milligram
mcg (µg) = microgramkg = kilogram
Volume L = liter (base unit)mL = millilitercc = cubic centimeter (not used anymore)
Length m = meter (base unit)cm = centimetermm = millimeter
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
The unit or abbreviation ALWAYS follows the amount,
put a space between them (lowercase except for L for
liters).
◦ Example: 5 g NOT g 5
Decimals are used to designate fractional metric units.
◦ Example: 1.5 mL NOT 1 ½ mL
Omit unnecessary zeros.
◦ Example: 1.5 g NOT 1.50 g
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
Use a zero to emphasize the decimal point for
fractional metric units of less than 1 (National
Patient Safety Goals). Example: 0.5 mg NOT .5 mg
◦ This is critical… It will prevent confusion &
potential dosage error. Think about what would
happened if overlooked the decimal point and
misinterpreted the medication order as 5 mg
instead of 0.5 mg. The dosage would be 10 times
too much. It could cause DEATH!!!!!!!!!!!
When in doubt, double check, DO NOT GUESS.
Ask the writer for clarification
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
Unit Abbreviation Equivalents
kilogram kg 1 kg = 1000 g
gram g
NOT Gm or gm
1 g = 1000 mg
milligram mg 1 mg = 1000 mcg
microgram mcg 0.001 mg = 1 mcg
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
Unit Abbreviation Equivalents
liter L
NOT ℓ
1 L = 1000 mL
milliliter mL
NOT mℓ
0.001 L = 1 mL = 1 cc
cubic
centimeter
Cubic
centimeter
1 cc
DO NOT USE LIST
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
Unit Abbreviation Equivalents
meter m 1 m = 100 cm = 1000 mm
centimeter cm 1 cm = 10 mm
millimeter mm 0.1 cm = 1 mm
1 inch = 2.5 cm
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
Unit Abbreviation Equivalents
grain gr gr i = 60 (65) mg
ounce oz 1 ounce = 30 mL
pint pt 16 oz = 500 mL
quart qt pt ii = 32 oz = 1000 mL = 1 L
Dram* 1 dram = 4 mL
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
a) .3g
b) 0.3 Gm
c) 0.3 g
d) .3 Gm
e) 0.30 g
a) .3g
b) 0.3 Gm
c) 0.3 g
d) .3 Gm
e) 0.30 g
a) 1 1/3 ml
b) 1.33 mL
c) 1.33 ML
d) 1 1/3 ML
e) 1.330 mL
a) 1 1/3 ml
b) 1.33 mL
c) 1.33 ML
d) 1 1/3 ML
e) 1.330 mL
a) 5 KG
b) 5.0 kg
c) kg 5
d) 5 kg
e) 5 kG
a) 5 KG
b) 5.0 kg
c) kg 5
d) 5 kg
e) 5 kG
a) Lasix 20.0 mg
b) Lasix 20 mg
c) Lasix 20 MG
d) Lasix mg 20
e) Lasix 20 Mg
a) Lasix 20.0 mg
b) Lasix 20 mg
c) Lasix 20 MG
d) Lasix mg 20
e) Lasix 20 Mg
Unit Abbreviation Equivalents
drop gtt Used for IV calculations
Teaspoon* t (or tsp) 1 t = 5 mL
Tablespoon* T (or tbs) 1 T = 3 t = 15 mL
ounce (fluid) oz 1 oz = 30 mL
ounce (weight) oz 1 lb = 16 oz
Cup* cup 1 cup = 8 oz = 240 mL
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
60 mggr i
gr ¼ 15 mg
gr ss30 mg
45 mg gr ¾
© 2004 Delmar Learning, a division of Thomson Learning, Inc.
ALL RIGHTS RESERVED.
To convert from a larger unit of measurement to a smaller one; MULTIPLY or move the decimal point to the right.◦ Example: 3 L = ? mL◦ THINK: Larger to Smaller: (×)◦ Equivalent: 1L = 1000mL Conversion factor 1000 3 L = ___mL 3 × 1000 = 3000 mL or move decimal 3 places to right
3L = 3.000 = 3000 mL
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
Convert 0.3 g to mg
(think 1 g = 1000 mg, conversion factor is 1000)
Think: Larger to smaller, MULTIPLY
Multiple by 1000: ◦ 0.3 g = 0.3 x 1000 = 300 mg
or move decimal 3 places to right ◦ 0.3 g = 0.300 = 300 mg
3-
23
To convert from a smaller unit of measurement to a larger one,DIVIDE or move the decimal point to the left.◦ Example: 400 mg = ? g◦ THINK: Smaller to Larger: ()◦ Equivalent: 1 g = 1000 mg (conversion factor = 1000)
400 mg = 400 1000 = 0.4 g Or move the decimal 3 places to the left 400 = 0.400 = 0.4 g
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
Convert 5000 mL to L
(think 1 L = 1000 mL, conversion factor is 1000)
Think: Smaller to Larger, DIVIDE
Divide by 1000: ◦ 5000 mL = 5000 ÷ 1000 = 5 L
or move decimal 3 places to left ◦ 5000 mL = 5.000 = 5 L
3-
25
You can use this diagram when converting dosages within the metric system.
MEMORIZE this too:
1 kg = 2.2 lb
© 2004 Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
kg g mg mcg
Move decimal point 3 places to the left for each step.
Move decimal point 3 places to the right for each step.
Can be used within the same system or between systems
Solving for X 8 mg = ___ g
1. State the known equivalent first, then add the incomplete ration to the other side, labeling all terms in the proportion
1000 mg: 1 g = 8 mg : x g
1. Solve for X (multiply inner terms, then outer terms)
◦ 1 X 8 = 1000 X x
◦ 8 = 1000 x
◦ 1 x 8=1000x X 1
◦ 1000 1000
◦ 8 = 1000 x
◦ 1000 1000
◦ X = 8/1000 = 0.008 g
◦ X = 0.008 g
Simpler to multiple or divide…
Solving for X 8 mg = ___ g
◦ Convert 8 mg = ___ g
◦ Approximate equivalent: 1g = 1000 mg
◦ Conversion factor is 1000
◦ Think: Smaller to larger, therefore divide (or move the decimal 3 places to the left)
8 mg = 8 ÷ 1000 = 0.008 g
To convert from a larger unit to a smaller unit of measure, you multiply by the conversion factor and To convert from a smaller to a larger unit of measure, you must divide by the conversion factor.
Example: Convert 45 mL to tApproximate Equivalent 1 t = 5 mL
Conversion factor = 5
THINK: Smaller to Larger so DIVIDE 45 / 5 = 9 t