# Linear Measurements on CT scans using Ruler tool

**URL:** <https://discourse.slicer.org/t/linear-measurements-on-ct-scans-using-ruler-tool/46586>\
**Category:** Community\
**Created:** [March 26, 2026, 7:01pm UTC](https://discourse.slicer.org/t/linear-measurements-on-ct-scans-using-ruler-tool/46586 "2026-03-26T19:01:57Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![egrady](https://avatars.discourse-cdn.com/v4/letter/e/f17d59/32.png) [@egrady](https://discourse.slicer.org/u/egrady)\
**Post date:** [March 26, 2026, 7:01pm UTC](https://discourse.slicer.org/t/linear-measurements-on-ct-scans-using-ruler-tool/46586/1 "2026-03-26T19:01:57Z")

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Hello!

I am exploring using 3D slicer for my dissertation. I am using CT (dicom) files of several bovid mandibles and need to take a linear measurement of tooth crown height. It seems like the best way to do this is using the ruler tool, but I want to make sure the measurement I’m getting is correct. My CTs are 0.5mm rather than 1mm - is there anything I need to adjust in 3D slicer to account for this? The scaling looks mostly correct as I took caliper height measurements too but is there anything else I need to adjust?

Thank you for any help you can provide!

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**Author:** ![pieper](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/pieper/32/8_2.png) [@pieper](https://discourse.slicer.org/u/pieper)\
**Post date:** [March 26, 2026, 7:21pm UTC](https://discourse.slicer.org/t/linear-measurements-on-ct-scans-using-ruler-tool/46586/2 "2026-03-26T19:21:35Z")

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That shouldn’t be a problem.

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**Author:** ![egrady](https://avatars.discourse-cdn.com/v4/letter/e/f17d59/32.png) [@egrady](https://discourse.slicer.org/u/egrady)\
**Post date:** [March 26, 2026, 7:28pm UTC](https://discourse.slicer.org/t/linear-measurements-on-ct-scans-using-ruler-tool/46586/3 "2026-03-26T19:28:36Z")

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So I can keep everything on their default settings? Jist load in my images and start measuring?

Thanks!

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**Author:** ![pieper](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/pieper/32/8_2.png) [@pieper](https://discourse.slicer.org/u/pieper)\
**Post date:** [March 26, 2026, 7:36pm UTC](https://discourse.slicer.org/t/linear-measurements-on-ct-scans-using-ruler-tool/46586/4 "2026-03-26T19:36:54Z")

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The ruler measurements will be in mm, so they already take into account the spacing of your source images. That all happens automatically. But since you are using these in your research you should sanity check anything you are relying on.

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**Author:** ![egrady](https://avatars.discourse-cdn.com/v4/letter/e/f17d59/32.png) [@egrady](https://discourse.slicer.org/u/egrady)\
**Post date:** [March 26, 2026, 7:41pm UTC](https://discourse.slicer.org/t/linear-measurements-on-ct-scans-using-ruler-tool/46586/5 "2026-03-26T19:41:30Z")

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Gotcha that makes sense but yes I will do so thank you for your help!