# Q- Surface area reported from Models: outward facing polys only?

**URL:** https://discourse.slicer.org/t/q-surface-area-reported-from-models-outward-facing-polys-only/11795
**Category:** Support
**Created:** [May 30, 2020, 2:27pm UTC](https://discourse.slicer.org/t/q-surface-area-reported-from-models-outward-facing-polys-only/11795 "2020-05-30T14:27:05Z")
**Posts on this page:** 1
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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 31, 2020, 1:02am UTC](https://discourse.slicer.org/t/q-surface-area-reported-from-models-outward-facing-polys-only/11795/3 "2020-05-31T01:02:06Z")

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You only need to divide the surface area by 2 if you want to measure area of an _open_ surface by creating a very flat _closed_ surface around it (as the closed surface wraps around both sides of the open surface).

For open surface measurements I would no longer recommend creating a closed surface and divide by 2, but instead you have better options, such as:

A. Use closed curve markups:

> [@How can I calculate an area on a CT image. I can calculate volumes (mm^3) but not areas (mm^2)](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-2/1549/4):
>
> In recent Slicer Preview Releases, you can draw curves and get their surface area (2D surface, as you would expect - only one side, no thickness). Select “Closed Curve” from the “Create and place” toolbar button: [image] Left-click on the image to place curve control points and right-click to finish placement: Measurements on curves are still work in progress, but you can open the Python console (Ctrl-3) and copy-paste the code below to see the surface area: curves=slicer.util.get…

B. Use cross section area measurement module:

> [@New module for measuring cross-section area of segments](https://discourse.slicer.org/t/new-module-for-measuring-cross-section-area-of-segments/11293):
>
> A new module - “Segment cross-section area” - has been added to Slicer. It can compute cross-sectional area of segmented structures along a chosen axis direction. Results are available both as a table and can be shown in a plot, too. Short demo video: For now, the module is available by installing “Sandbox” extension in the extension manager in a recent 3D Slicer Preview Release. If you have any comments and suggestions then please post it here.

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