# Feature Request: Weight Percents

**URL:** <https://openmc.discourse.group/t/feature-request-weight-percents/26>\
**Category:** User Support\
**Created:** [June 21, 2013, 1:24am UTC](https://openmc.discourse.group/t/feature-request-weight-percents/26 "2013-06-21T01:24:00Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Terry\_Price](https://avatars.discourse-cdn.com/v4/letter/t/f475e1/32.png) [@Terry\_Price](https://openmc.discourse.group/u/Terry_Price)\
**Post date:** [June 21, 2013, 1:24am UTC](https://openmc.discourse.group/t/feature-request-weight-percents/26/1 "2013-06-21T01:24:00Z")

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Hey Guys (the devs in particular),

Do you think in a future release, you might make it possible to specify isotope fractions by weight fractions as well?

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**Author:** ![paulromano](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/paulromano/32/486_2.png) [@paulromano](https://openmc.discourse.group/u/paulromano)\
**Post date:** [June 21, 2013, 1:38am UTC](https://openmc.discourse.group/t/feature-request-weight-percents/26/2 "2013-06-21T01:38:53Z")

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Hi Terry- You just need to give wo="…" instead of ao="…" on a element. See:  
[http://mit-crpg.github.io/openmc/usersguide/input.html#material-element](http://mit-crpg.github.io/openmc/usersguide/input.html#material-element)

Best regards,  
Paul

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**Author:** ![Terry\_Price](https://avatars.discourse-cdn.com/v4/letter/t/f475e1/32.png) [@Terry\_Price](https://openmc.discourse.group/u/Terry_Price)\
**Post date:** [June 21, 2013, 2:39am UTC](https://openmc.discourse.group/t/feature-request-weight-percents/26/3 "2013-06-21T02:39:04Z")

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Huh, I could have sworn I read that article…weird…