# Why my 3D-printed model doesn't match the real size?

**URL:** https://discourse.slicer.org/t/why-my-3d-printed-model-doesnt-match-the-real-size/19688
**Category:** Support
**Tags:** 3d-printing
**Created:** [September 15, 2021, 6:23pm UTC](https://discourse.slicer.org/t/why-my-3d-printed-model-doesnt-match-the-real-size/19688 "2021-09-15T18:23:59Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![arezoo.movahed](https://avatars.discourse-cdn.com/v4/letter/a/958977/32.png) [@arezoo.movahed](https://discourse.slicer.org/u/arezoo.movahed)
#### Post date: [September 15, 2021, 6:24pm UTC](https://discourse.slicer.org/t/why-my-3d-printed-model-doesnt-match-the-real-size/19688/1 "2021-09-15T18:24:00Z")

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Hello,  
I remodel a human heart, actually I used my Mom’s CT Angiography data, and after segmentation, I exported a stl file and 3D-Print it.  
But the model is so big and doesn’t match the real size.  
I was wondering what should be done before exporting the stl file to have the real size?  
Your prompt response is highly appreciated.  
Sincerely,  
Arezoo

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### Author: ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [September 15, 2021, 6:27pm UTC](https://discourse.slicer.org/t/why-my-3d-printed-model-doesnt-match-the-real-size/19688/2 "2021-09-15T18:27:55Z")

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The STL files that Slicer creates from DICOM CT files uses millimeter as unit by default. You can change that by specifying a custom “Size scale” in the “Export segments to files” window:

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/2/9/29726b60be4928b228bf207ce71adc8d02f780fa.png)

If you want the file to contain coordinate values in meter then set size scale to 0.001.

Make sure that you chose the corresponding unit in your 3D printing software.