# 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")\
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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:** [May 18, 2021, 5:52pm 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-2/1549/24 "2021-05-18T17:52:23Z")

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If you segmented a single slice and the slice is so thick that the area of the side wall is not negligible (this should be very rare) then you can compute the circumference and cross-section area from the known volume, surface area, and slice thickness with a simple formula (because you have two unknowns `cross_section_area` and `circumference` and two equations: `volume = cross_section_area * slice_thickness` and `surface_area = 2 * cross_section_area + circumference * slice_thickness`).

Alternatively, you can also use [Segment Cross-Section Area](https://discourse.slicer.org/t/new-module-for-measuring-cross-section-area-of-segments/11293) module as described above (this is mostly useful if you have segmented on many slices).

In the future, you can measure 2D surface area directly using Closed curve markups:

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/9/c/9c1f878ed57053691e50691f2145e5ba534e0ca6.jpeg)

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