Medical Math Skills USA

one ounce

30 ml

one dram

4 ml

one ml

15 min (minums)

one minum

one gtt (drop)

one tablespoon (T)

15 ml

one teaspoon (t)

5 ml

one grain (gr)

60 mg

gr 15 is equal to mg

gr 15 : X mg = gr 1 : 60 mg

12 dram to ml

12 dram : X ml = 1 dram : 4 ml

3 ounces to T

3 oz : X T = 1 oz : 2 T

2 t to X ml

2 t : X ml = 1 t : 5 ml

gr 10 to mg

gr 10 : X mg = gr 1 : 60 mg

gr 1/2 = mg

answer 30 mg

8 ml = dr

answer 2 drams

gr 1/6 = mg

answer 10 mg

Convert C to F

multiply C by 9/5 then add 32 (remember C is smaller so we add 32)

Convert F to C

subtract 32 from F then multiply by 5/9 (remember F is bigger so we subtract 32)

Formula method

Want (dr order) over Have (what you have on hand) times what have is in (mls or tabs)

Ratio

2mg : 1ml = X mg : 5 ml.

Multiply the two numbers without the X and then divide by the one with the X. Ex 2 times 5 divided by one=10

(remember the means or middles times themselves and the extremes or ends times themselves)

to convert within the metric system

Bigger to smaller move the decimal three places to the right. Smaller to bigger move the decimal three places to the left.

Bigger to smaller

Kg g mg mcg

move decimal three places to the right

Smaller to bigger

mcg mg g Kg

move decimal three places to the left

when doing any problem

make sure all numbers are within the same measurement ie mg, ml, Kg,

You can NOT work with numbers from two different areas until you make them the same ie

0.7 g and 45 mg (move the bigger number's decimal to the right three spaces so they are both mg. you can also move the smaller number three places to the left but it does not make it easier) 700 mg and 45 mg is easier than .7 g and .0045 g

make sure you are within the same system when beginning your calculations

you can't use unlike numbers

ie 3 t when your bottle reads in mls. you need to understand how mls and t compare so that you can give the correct dose.

1t is = to 5 ml

do a ratio problem to get the correct equivalent

3t : X mls = 1t : 5 mls(make sure like numbers are on the same side of the problem such as t on left and mls on right)

multiply the two whole numbers; in this case 5 times three and divide them by the remaining number of 1

give 15 mls (always be sure to include the measure that followed X)

hourly IV dose

when you read an order for 1000 mls over 8 hours you must divide by the total hours to get the mls per hour: in this case 125 mls per hour

IV administration

can be done by infusion pump or calculated by drop factor and regulated by a drip chamber and roller clamp

IV drop factor

the amount of drops per ml depends on the size of the hole in the drip chamber. these numbers vary per manufacturer and can come in 10 gtt/ml, 15 gtt/ml, or 20gtt/ml or micro drip which is 60gtt/ml (this is the same drop factor for infusion pumps)

calculation of IV drip rates

quantity to infuse multiplied by the drop factor divided by total infusion time in minutes; over 60 minutes, 90 minutes, 30 minutes (as long as the time is in minutes)

ie125 mls to infuse over 90 minutes with a drop factor of 15; 125 times 15 to get total drops then divide by the quantity of minutes in which it should infuse.

100 mls to infuse over 10 hours via a drop factor of 20

remember to divide by 10 hours to get a 60 minute quantity

now multiply the 60 minute quantity by the drop factor of 20

now divide the answer by 60 minutes to the drip rate you should regulate your clamp to

drop factor of infusion pump

60 gtt/ml

if you have an hourly rate you multiply it by 60(infusion pump gtt factor) then divide it by 60 minutes to get the rate you would set the pump to. ie 80 ml per hour times 60 gtt/ml divided by 60 minutes equals 80 (if you are infusing over one hour you just enter the amount per hourp

250 ml to infuse over 90 minutes (now you have to do the math) 250 times drop factor of 60 times 90 minutes. do the math.