Question about Equivalents...HELP!

darned liberal · Jun 27, 2005

You are correct. 1 gram ≈ 15.4323584 grain. They taught us in LPN school that 0.9 is close enough to 1. An ounce is not exactly 30cc either but that's the accepted conversion because it's just too freakin' hard to do calculations out to 7 decimal places if you're not going to get anyone lost in space over it.

Here is a neat online conversion tool I found researching your question:

http://www.onlineconversion.com/weight_common.htm

The most common example of grains/milligrams is tylenol and aspirin. They both come in 325mg tablets. Old school docs wrote X grains, meaning 650mg. No, 10 grains does not equal 650mg but can you break off 4mg from a 325mg tablet? If it were a perfect equivalent then 1 gram of tylenol would be 15 grains or 1000mg. But today when a doctor asks for a gram of tylenol, we can give 1000mg or 3 x 325, it doesn't really matter. An extra 50mg will not cure them and the old school dose was 15 grains anyway. That would be ≈972mg; right in between!

Keep being a perfectionist. Nursing instructors love it.

Megs7617 · Jun 27, 2005

thanks! I feel so happy that I was right! :)

now, is that why the table that my school gave us says that 8 ounces equals 240 mL, then on the next line it says that 16 ounces equals 500 mL???

I was confused because I would just assume that if 8 ounces equals 240 mL, then wouldnt 16 ounces equal 480 mL???

Also, thanks for the website, Im going to check it out right now. I also came across a neat one while looking for the answer to my first question. I posted it in one the stickies, I think the one about dosage calculations.

darned liberal · Jun 27, 2005

thanks! I feel so happy that I was right! :)
now, is that why the table that my school gave us says that 8 ounces equals 240 mL, then on the next line it says that 16 ounces equals 500 mL???
I was confused because I would just assume that if 8 ounces equals 240 mL, then wouldnt 16 ounces equal 480 mL???
Also, thanks for the website, Im going to check it out right now. I also came across a neat one while looking for the answer to my first question. I posted it in one the stickies, I think the one about dosage calculations.

Yes, when you're close enough to compare ounces to liters, you do that. So a cup is 240, but two cups is 500. That's for liquid intake.

Output is always multiples of 10 or 25 because that's where the marks are on the graduated cylinder, unless you have a meter that will read single ccs (and you need to be so specific).

Megs7617 · Jun 27, 2005

:) i see....

thanks for the help...i am very grateful :)

stargazer109 · Jul 16, 2008

I had brought this problem up with my teacher and she had no answers. An example is 5g = ? gr. If you use the 15gr=1g method you get 75 grains, if you use the conversion method with 1gr=60mg you would get 83.3! Here is the best way to figure out the answer.

When converting:

Grams to Grains = multiply by 15

Grains to Grams = divide by 15

Grains to Milligrams = multiply by 60

Milligrams to Grains = divide by 60

So far, the answers have come out perfectly with this method. The big problem is that schools are teaching 60mg=1grain, but actually 1 grain = 64.8mg. That is why you are getting different answers.

Hope this helps!

Tharem · Jul 21, 2008

The real issue is that the Apothecary and Household systems are not as mathematically exact as the metric system. You may find near exact equivalents published in some places, such as 1 gram ≈ 15.4323584 grain but those values were created just for mathematical rigor and were never actually used when the Apothecary system was in wide use.

The Apothecary and Household systems are really holdovers from an earlier time and are rarely used in practice anymore. Where they are used, it is only in cases where the discrepancy between units is not significant, such as aspirin dosage. In medications where exact dosage is critical you'll never see those systems used. so the approximate conversion factors are acceptable.

The only rules to remember with regards to Apothecary and Household systems as far as your tests go is to use the conversion factors they teach at your school, and when calculating number of tablets or pills to give, use the nearest equivalent mg dose per tablet or fraction of tablet in the case of scored tablet. Never split non-scored or time release tablets.