Nursing Math Tutorial

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Metric Nursing Conversions

1 kilogram (kg)	=	2.2 pounds (lb)
1 pound (lb)	=	453.6 grams (g or gm) (use 454)
1 kilogram (kg)	=	1000 grams (g or gm)
1 gram (g or gm)	=	1000 mg (milligrams)
1 milligram (mg)	=	1000 micrograms (mcg)
1 gram (gm)	=	1 ml (milliliter) [Preferred term]
1 cc (cubic centimeter)	=	1 ml (milliliter)
1 inch (in)	=	2.54 cm (centimeters)
1 grain (gr)	=	60 mg (milligrams)
1 (household) cup	=	240 ml (milliliter)
8 ounces (oz)	=	1 (measuring) cup
16 ounces (oz)	=	1 pint (pt)
1 ounce (oz)	=	30 ml (milliliter)
1 teaspoon (tsp)	=	5 ml (milliliter) (not 4-5)
1 dram	=	4 ml (milliliter) [archaic use]
1 tablespoon ( T or tbs)	=	15 ml (milliliter)
2 tablespoons (T or tbs)	=	1 Ounce
3 teaspoons (tsp)	=	1 tablespoon ( T or tbs)
1 teaspoon (tsp)	=	75 gtt (drops)
1 milliliter (ml)	=	16 minims (not 15-16)
1 milliliter (ml)	=	15 gtt (drops)
1 liter (L)	=	1000 ml (milliliter)
37.0 ° C (Centigrade degrees)	=	98.6° F (Fahrenheit degrees)

How to Calculate Fluid Dosages

This formula is used to calculate the the amount of medication in solution for oral, intamuscular, intravenous, or subcutaneous injection to be administered when given a doseage, stock dose and volume.

Desired Dose
----------------------
Available Dose

Multiplied by

Quantity
----------------------
1

= Volume to be given

Example1: A client is ordered 15mg of Troymoral. You have 2ml of solution on hand which contains 25 mg Troymoral. What volume of solution would you give?

15 mg
-------------
25 mg

2 mg
---------
1 ml

30
------
25

= 1.2 ml

Example 2: A dose of 75 mg of Lizagrafin has been ordered. It is available in ampoules containing 100 mg in 2 ml. What volume must be administered?

75 mg
-------------
100 mg

2 ml
------
1 ml

150
---------
100

= 1.5 ml

How to Calculate Tablet Dosages

Use this formula is used to calculate the number of tablets to be used when given the required dose. Remember, the dosage amount must be the same.

Desired Dose
------------------
Available Dose = Number of tablets to be given

Example 1: A client is ordered 300mg of a pain reliever. 600 mg tablets are available. How many tablets would you give?

300 mg
------------------
600 mg

= 1/2 tablet

Example 2: How many tablets containing 62.5 mcg will be required to give a dose of 0.125 mg?

STEP 1 : CONVERT TO SAME UNITS

Convert 0.125 mg to mcg by moving the decimal 3 places to the right.

0.125 mg = (0.125 * 1000 mcg) = 125 mcg

STEP 2: CALCULATE

125 mcg
------------------
62.5 mcg

= 2 tablets

How to Calculate IV Flow Rates

Intravenous fluid must be given at a specific rate, neither too fast nor too slow. The specific rate may be measured as ml/hour, L/hour or drops/min. To control or adjust the flow rate only drops per minute are used.

The burette contains a needle or plastic dropper which gives the number of drops per ml (the drop factor). A number of different drop factors are available (determined by the length and diameter of the needle).

Common drop factors are:

10 drops/ml (blood set), 15 drops / ml (regular set), 60 drops / ml (microdrop).

To measure the rate we must know:

(1) the number of drops
(2) time in minutes.

The formula for working out flow rates is:

volume (ml) X drop factor (gtts / ml)
---------------------------------------------
time (min)

= gtts / min (flow rate)

Example: 1500 ml IV Saline is ordered over 12 hours. Using a drop factor of 15 drops / ml, how many drops per minute need to be delivered?

1500 (ml) X 15 (gttss / ml)
---------------------------------------------------
12 x 60 (gives us total minutes)

= 31 gtts / minute

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