Cu inchs & gcc = ? lbs for the math challenged

Factual Questions
1

Hi

I need to find the weight (lbs or grams) of a plastic part that I only have a drawing of. I have the Part volume ( .629 cu in. ). The density of the material is 1.14 g/cc ( which I think is grams/centimeter?). How do I calculate the lbs or grams?

thanks for your help!

Bob Z

2

Well, the unit you want is grams, so set up the equation so that the cc’s cancel out. Hope that helps you solve it yourself. :slight_smile:

3

I don’t do homework but multiply volume by density (all in the correct units) and you should have your answer.

Actually, I will do homework if you pay me well enough :slight_smile:

4

I didn’t notice the part volume is in cubic inches. Convert to cubic centimters by multiplying by 16.37.

5

Thanks for the input, its not home work by the way ( I graduated VoTec in 1980, we really didn’t do much math). I now at work though its 1.25 hrs after quitting time working on this “project”.

I got an answer of 15.15 grams by

.629 cu in x 16.3871 = 10.31 cubic centimeters

10.31 cc x 1.47 g/cc = 15.15 grams

Its just I want to make sure its done right.

Thanks
BobZ

6

It could be homework. But then again, it might not be. Some people really can’t solve a simple problem like this, so I’d rather help them than not.

0.629 in3 * (16.387064 cm3/in3) = 10.30746 cm3

1.14 grams/cm3 * 10.30746 cm3 = 11.751 grams

Since you only have 3 significant digits, this is 11.8 grams

To convert to lbm:

11.8 grams * 0.0022046 lbm/gram = 0.0260 lbm

7

Then you need to check that density to make sure you didn’t mess up here - you had “1.14 g/cc” in the OP. :confused:

8

I think Google can do this for you with its new calculator function?

Search for 1.14grams/cubic cm*.629 cubic in in pounds there.

Is that answer right?

9

Thanks again for your help and very quick reply. You are correct the number should of been 1.47. (this is why I also screw these things up) .

Well Its late I’m going home, most likely to help the kids with their home work.

thanks
Bob Z

10

Here is a great calculator for figuring out a density, volume and mass problem.
http://www.1728.com/density.htm
Input 2 of the 3 variables and the 3rd is calculated.
Mass can be input in terms of 9 units (grams, pounds tons, etc) and the same applies to volume and density.
Give it a try.
I got .0259 pounds which agrees with Una Perrson’s calculation.