# How can I calculate an area on a CT image. I can calculate volumes (mm^3) but not areas (mm^2)

**URL:** https://discourse.slicer.org/t/how-can-i-calculate-an-area-on-a-ct-image-i-can-calculate-volumes-mm-3-but-not-areas-mm-2/1549
**Category:** Support
**Created:** [November 28, 2017, 9:09pm UTC](https://discourse.slicer.org/t/how-can-i-calculate-an-area-on-a-ct-image-i-can-calculate-volumes-mm-3-but-not-areas-mm-2/1549 "2017-11-28T21:09:20Z")
**Posts on this page:** 1
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### Author: ![TANG](https://avatars.discourse-cdn.com/v4/letter/t/e8c25b/32.png) [@TANG](https://discourse.slicer.org/u/TANG)
#### Post date: [August 18, 2019, 3:21pm UTC](https://discourse.slicer.org/t/how-can-i-calculate-an-area-on-a-ct-image-i-can-calculate-volumes-mm-3-but-not-areas-mm-2/1549/3 "2019-08-18T15:21:11Z")

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A single layer of the same dicom has different surface areas with different layers thickness (1mm,3mm,5mm), resulting in a large difference in surface area between the two.

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