# Particle number when using weight window

**URL:** <https://openmc.discourse.group/t/particle-number-when-using-weight-window/2809>\
**Category:** User Support\
**Created:** [March 8, 2023, 5:33am UTC](https://openmc.discourse.group/t/particle-number-when-using-weight-window/2809 "2023-03-08T05:33:40Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Kimberly](https://avatars.discourse-cdn.com/v4/letter/k/f4b2a3/32.png) [@Kimberly](https://openmc.discourse.group/u/Kimberly)\
**Post date:** [March 8, 2023, 5:33am UTC](https://openmc.discourse.group/t/particle-number-when-using-weight-window/2809/1 "2023-03-08T05:33:40Z")

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Hi all. I want to know number of particles per fission source iteration when both element and weight window are given in a k-eigenvalue calculation. For example, I specify the weight of particles in all grids as 1E-9, and the element as 1E6. How many neutrons does OpenMC simulate per iteration?

Any help regarding this topic would be very appreciated.

Kimberly