# Metric conversions help! - page 2

We are having to use the metric, apothecary, and household systems and convert between them all . Im stuck on the ones that are fractions.....how do I convert these? Thanks sooooo much 1/8... Read More

1. Quote from Daytonite
Here is how to do these problems utilizing conversion factors and using dimensional analysis. Please note that depending on the conversion factors you use when going between grams and grain there will be variances in the answers:

you want to end up with the final label of mg in the numerator. Also, convert 1/8 to a decimal of 0.125 which was done for you in a previous post just to make things easier. So, the DA equation will be set up like this:
0.125grains / 1 (given information) X 60mg / 1 grain (conversion factor set up so that the labels, "grain", will cancel out from the numerator of one fraction and the denominator of the other leaving you with only one label, "mg") = 7.5mg

you want to end up with the final label of grams in the numerator.
3.2kg / 1 (given information) X 1000grams / 1kg (conversion factor, again set up so that the labels, "kg" will cancel out leaving you with only the label of "grams") = 3200 grams

you want to end up with the final label of cc (cubic centimeters) in the numerator
2.42 L(liters) / 1 (given information) X 1000mL / 1L (conversion factor) X 1cc / 1mL (conversion factor) = 2420 cc

you want to end up with the final label of grains in the numerator
0.03grams / 1 (given information) X 15grains / 1gram (conversion factor) = 0.45 grains

you want to end up with the label of lb.(pounds) in the numerator
6oz (ounces) / 1 (given information) X 1 pound / 12 ounces (conversion factor) = 0.5 pounds

You are doing ratio/proportion, right? It sure looks like it thou..
2. Bala Shark. . .I prefaced what I did by saying I was doing the problems by dimensional analysis. In dimensional analysis, or the factor label method, you are setting up a series of fractions (which you can also call ratios) and manipulating the numerators and denominators of all the terms, including the conversion factors, with the very specific purpose of being able to factor out the duplicated "labels" that go with the numbers. Your sole purpose is to first be left with the labels you want to be left with in the end. Then, you start doing the math with the numbers.
3. so multiply when going from big to small unit and divide when going from small to big??
4. Quote from FNPhopeful
so multiply when going from big to small unit and divide when going from small to big??
It is like saying it you times:

1 grain = 60 mg
2 grains = ? mg
2 x 60 = 120
2 grains = 120 mg

Here is when you divide

kg = 2.2 pounds
4.4 pounds = ? kg
4.4/2.2 = 2
4.4 pounds = 2 kg

It is something like that, but you have to know the conversions by heart..
5. Quote from fnphopeful
so multiply when going from big to small unit and divide when going from small to big??
look at how i worked out the problems for you. where did you see me do any division in any of them? no where. i never went from big to small units either. i went from one label, such as "grains" to "mg". with dimensional analysis you set up fractions and multiply them together. all i did was manipulate the numerators and denominators of the conversion factors or the given information in order to factor out the duplicated labels and end up with a final answer that has the label on it that was wanted. each conversion factor is an identity so that no matter which part is in the numerator or the denominator, it is still a ratio whose top and bottom are equal to each other--therefore the fraction can be flipped if need be in order to factor out unwanted labels. (for example: 1 min/60 seconds is just the same as 60 seconds/1 min) please read those two sentences over and over until it sinks in and you understand what they are saying. until you understand that, you are not going to be able to do these conversions by the method i have shown you.

here is a paper on dimensional analysis:
http://www-isu.indstate.edu/mary/tutorial.htm - from the indiana state university a "basics" page on medication math with explanations on how to do a number of different types of medications problems using dimensional analysis
6. Daytonite, I am not attacking the way you do your problems but some students might find your way of doing the problems more difficult because you are applying ratio/proportion in your method..
7. Daytonite, This is how I learned to set up the problems and boy did it make it so much easier! I have always breezed through these math problems while others sat there looking at me. My chemistry instructor tried teaching the class to use this system and most of the class sat there looking dumb founded. I guess everyone has a different way of learning things. I never once missed a chemistry problem using this set up, so I am hoping that my luck continues on into the nursing math.

Beth
8. Quote from Bala Shark
Daytonite, I am not attacking the way you do your problems but some students might find your way of doing the problems more difficult because you are applying ratio/proportion in your method..
I am not at all offended. I am just showing another way to do these problems--that's by dimensional analysis, factor label method. I often will show how problems are solved this way because it is not often demonstrated although it is talked about on the forums. In practice, I use another method myself. I am just showing another way to do these problems. It helps to know one or two ways. It's a good way to double check your answers, for one thing. Please, especially FNPhopeful, do not feel like you need to do these problems the way I have shown. If there is another way that is easier for you and gets you to the right answer, then that is what you should do. The bottom line is getting the right answer.
9. That's the way I learned it also Daytonite.
However, we also had an "option" of a grain being 60, 64 or 65 mg..........And then there were minims.....anybody remember those?
10. Quote from P_RN
And then there were minims.....anybody remember those?
Depends which system you use:

1.British imperial : A measure (liquid or dry) equal to 1/60th fluid dram or 0.059194 cubic centimeters

2. United States: liquid unit equal to 1/60 fluidram

Personally, I wish we'd all switch to SI systems (or atleast, pick ONE system and stick to it) and be done with it. Might help reduce some of our med errors!
11. I learned by dimensional analysis as well.

1 mg = 1000 mcg
60 mg = 1 grain
1000 mg= 15 grains = 1 gram
1ml = 15 gtts = 15 Minims
5 ml = 1 dram = 1 tsp = 60 gtts = 60 Minims
30 ml = 8 drams = 1 oz = 2 Tbsp
240 ml = 8 oz = 1 cup

also, 1 ml = 60 microdrops in soluset

Those are the conversions I wrote at the top of my tests, and it's worked like a charm. I added a bunch more for peds. stuff this semester, but the basics are there.

HTH!