# Are measurements in slicer calculated by the DICOM file? How do you know it is accurate?

**URL:** <https://discourse.slicer.org/t/are-measurements-in-slicer-calculated-by-the-dicom-file-how-do-you-know-it-is-accurate/34887>\
**Category:** Support\
**Created:** [March 14, 2024, 11:27am UTC](https://discourse.slicer.org/t/are-measurements-in-slicer-calculated-by-the-dicom-file-how-do-you-know-it-is-accurate/34887 "2024-03-14T11:27:53Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![bw3232](https://avatars.discourse-cdn.com/v4/letter/b/43a26b/32.png) [@bw3232](https://discourse.slicer.org/u/bw3232)\
**Post date:** [March 14, 2024, 11:27am UTC](https://discourse.slicer.org/t/are-measurements-in-slicer-calculated-by-the-dicom-file-how-do-you-know-it-is-accurate/34887/1 "2024-03-14T11:27:53Z")

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Hi All,

When using 3d Slicer’s ruler/ markdown tools, I was wondering how the measurement is actually calculated. Is the relative scale captured in the DICOM file? (For example, how does 3D slicer know what 1mm is on each subject).

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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:** [March 17, 2024, 2:09am UTC](https://discourse.slicer.org/t/are-measurements-in-slicer-calculated-by-the-dicom-file-how-do-you-know-it-is-accurate/34887/2 "2024-03-17T02:09:45Z")

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Yes, full 3D geometry (origin, spacing, axis directions) are specified in the DICOM files.