# Finding either moles \[mol\] or mass \[kg\] of protein dissolved in water

**URL:** <https://gromacs.bioexcel.eu/t/finding-either-moles-mol-or-mass-kg-of-protein-dissolved-in-water/789>\
**Category:** User discussions\
**Created:** [September 9, 2020, 3:33pm UTC](https://gromacs.bioexcel.eu/t/finding-either-moles-mol-or-mass-kg-of-protein-dissolved-in-water/789 "2020-09-09T15:33:22Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![wcc6571](https://avatars.discourse-cdn.com/v4/letter/w/e5b9ba/32.png) [@wcc6571](https://gromacs.bioexcel.eu/u/wcc6571)\
**Post date:** [September 9, 2020, 3:33pm UTC](https://gromacs.bioexcel.eu/t/finding-either-moles-mol-or-mass-kg-of-protein-dissolved-in-water/789/1 "2020-09-09T15:33:22Z")

</div>

GROMACS version: 2020  
GROMACS modification: Yes/No

Hello, I have a simple protein in water system. Which command should I use to find out the number of moles of the protein (or alternatively mass) in the system I have? Thanks in advance.

---

<div class="post-metadata">

**Author:** ![pjohansson](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/pjohansson/32/316_2.png) [@pjohansson](https://gromacs.bioexcel.eu/u/pjohansson)\
**Post date:** [September 10, 2020, 11:12am UTC](https://gromacs.bioexcel.eu/t/finding-either-moles-mol-or-mass-kg-of-protein-dissolved-in-water/789/2 "2020-09-10T11:12:53Z")

</div>

You can calculate the mass by calculating the density profile of the protein with `gmx density`, then integrate the profile over your box. Or by reading the protein structure and add atom masses using a script.

---

<div class="post-metadata">

**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\
**Post date:** [September 10, 2020, 1:01pm UTC](https://gromacs.bioexcel.eu/t/finding-either-moles-mol-or-mass-kg-of-protein-dissolved-in-water/789/3 "2020-09-10T13:01:57Z")

</div>

`gmx editconf` will report the mass of the system. So you can do a dummy operation like `gmx editconf -f conf.gro -o tmp.gro` and it will print the mass to the terminal.

The number of moles is easier. If there’s one protein molecule then you have (1/6.022 x 1023) moles in the system.