# Heat transfer unit dimensions in (N \* mm)?
**URL:** https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837
**Category:** Uncategorized
**Created:** [September 23, 2023, 5:42pm UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837 "2023-09-23T17:42:00Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@Awareness](https://calculix.discourse.group/u/Awareness)
#### Post date: [September 23, 2023, 5:42pm UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837/1 "2023-09-23T17:42:00Z")
I used units as per ccx Table 1: Frequently used units in different unit systems. mm, N, s, K and I get stupefied with achieved heat transfer unit dimensions.
Body is a cube.
Excerpt from ccx manual “Now, since force = mass × length / time2 , we get that mass = force × time2/length. This leads to Ns2 /mm for the mass and Ns2 /mm4 for density.”
Or my formulas are not for use with the unit system mm, N, s, K, aren’t they?
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### Author:  [@rsmith](https://calculix.discourse.group/u/rsmith)
#### Post date: [September 23, 2023, 6:20pm UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837/2 "2023-09-23T18:20:09Z")
My advice would be to stick to SI units [m,kg,s,K].
Then density is kg/m3, thermal conductivity is W/(mK) and specific heat is J/(kgK).
It will make your calculations less error-prone if you don’t have to do all kinds of conversions.
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### Author:  [@Awareness](https://calculix.discourse.group/u/Awareness)
#### Post date: [September 23, 2023, 6:24pm UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837/3 "2023-09-23T18:24:20Z")
I gave it a deep thought but I did not find how to do geometry in meters or centimeters. cgx / ccx are unit less though.
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### Author:  [@rsmith](https://calculix.discourse.group/u/rsmith)
#### Post date: [September 23, 2023, 6:47pm UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837/4 "2023-09-23T18:47:59Z")
> [@Awareness](#):
>
> I did not find how to do geometry in meters
Just specifiy distances and lengths in meters.
For example in the preprocessor file for `cgx`, you can do simple calculations when you define values, e.g. to convert [mm] to [m]:
```auto
# Body sides
valu a1 / 10 1000
valu a2 / 10 1000
# Body depth
valu d / 3 1000
# Temperature
valu Ti + 25 273.15
```
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### Author:  [@Awareness](https://calculix.discourse.group/u/Awareness)
#### Post date: [September 23, 2023, 7:02pm UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837/5 "2023-09-23T19:02:33Z")
Strange thing I did not think of conversion at all, I thought of something else. What it is that else, no idea.
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### Author:  [@Calc\_em](https://calculix.discourse.group/u/Calc_em)
#### Post date: [September 23, 2023, 7:37pm UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837/6 "2023-09-23T19:37:53Z")
This table from Abaqus documentation can help you keep unit consistency:
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### Author:  [@Awareness](https://calculix.discourse.group/u/Awareness)
#### Post date: [September 23, 2023, 8:28pm UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837/7 "2023-09-23T20:28:11Z")
Thank you for your reply.
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### Author:  [@Disla](https://calculix.discourse.group/u/Disla)
#### Post date: [September 23, 2023, 9:13pm UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837/8 "2023-09-23T21:13:05Z")
A unit converter could be very useful too.
There are many out there.
I have been using Uconeer 2.4 for many years as it is super complete and free.
Not sure if you can still find it somewhere. Subsequent versions ended up being paid for.
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### Author:  [@Calc\_em](https://calculix.discourse.group/u/Calc_em)
#### Post date: [September 24, 2023, 8:56am UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837/9 "2023-09-24T08:56:09Z")
Even Google can handle basic unit conversions but for more advanced cases you can use e.g. Wolfram Alpha, SMath or Calcpad.
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### Author:  [@Awareness](https://calculix.discourse.group/u/Awareness)
#### Post date: [September 24, 2023, 11:08am UTC](https://calculix.discourse.group/t/heat-transfer-unit-dimensions-in-n-mm/1837/10 "2023-09-24T11:08:50Z")
@Disla, Calc\_em I note your suggestions, thanks both of you.