# Cu inchs & gcc = ? lbs for the math challenged **URL:** \ **Category:** Factual Questions\ **Created:** [October 2, 2003, 9:11pm UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210 "2003-10-02T21:11:14Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![robz](https://avatars.discourse-cdn.com/v4/letter/r/ac8455/32.png) [@robz](https://boards.straightdope.com/u/robz)\ **Post date:** [October 2, 2003, 9:11pm UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210/1 "2003-10-02T21:11:14Z")
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 ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [October 2, 2003, 9:13pm UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210/2 "2003-10-02T21:13:34Z")
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. 🙂 ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [October 2, 2003, 9:14pm UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210/3 "2003-10-02T21:14:27Z")
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 🙂 ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [October 2, 2003, 9:16pm UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210/4 "2003-10-02T21:16:50Z")
I didn’t notice the part volume is in cubic inches. Convert to cubic centimters by multiplying by 16.37. ---
**Author:** ![robz](https://avatars.discourse-cdn.com/v4/letter/r/ac8455/32.png) [@robz](https://boards.straightdope.com/u/robz)\ **Post date:** [October 2, 2003, 10:07pm UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210/5 "2003-10-02T22:07:30Z")
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 ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [October 2, 2003, 10:11pm UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210/6 "2003-10-02T22:11:05Z")
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 ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [October 2, 2003, 10:12pm UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210/7 "2003-10-02T22:12:31Z")
> [@](#): > > \*Originally posted by robz \* > \*\*10.31 cc x 1.47 g/cc = 15.15 grams > > Its just I want to make sure its done right.\*\* 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. 😕 ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [October 2, 2003, 10:26pm UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210/8 "2003-10-02T22:26:52Z")
I think Google can do this for you with its new calculator function? Search for [1.14grams/cubic cm\*.629 cubic in in pounds](http://www.google.com/search?num=100&hl=en&lr=&ie=ISO-8859-1&safe=off&q=1.14grams%2Fcubic+cm*.629+cubic+in+in+pounds) there. Is that answer right? ---
**Author:** ![robz](https://avatars.discourse-cdn.com/v4/letter/r/ac8455/32.png) [@robz](https://boards.straightdope.com/u/robz)\ **Post date:** [October 2, 2003, 10:34pm UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210/9 "2003-10-02T22:34:47Z")
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 ---
**Author:** ![wolf\_meister](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolf_meister/32/15202_2.png) [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)\ **Post date:** [October 3, 2003, 2:53am UTC](https://boards.straightdope.com/t/cu-inchs-gcc-lbs-for-the-math-challenged/205210/10 "2003-10-03T02:53:50Z")
Here is a great calculator for figuring out a density, volume and mass problem. [http://www.1728.com/density.htm](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.