# RDF confusing

**URL:** <https://gromacs.bioexcel.eu/t/rdf-confusing/4849>\
**Category:** User discussions\
**Created:** [September 23, 2022, 2:36pm UTC](https://gromacs.bioexcel.eu/t/rdf-confusing/4849 "2022-09-23T14:36:07Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![shiva](https://avatars.discourse-cdn.com/v4/letter/s/85e7bf/32.png) [@shiva](https://gromacs.bioexcel.eu/u/shiva)\
**Post date:** [September 23, 2022, 2:36pm UTC](https://gromacs.bioexcel.eu/t/rdf-confusing/4849/1 "2022-09-23T14:36:07Z")

</div>

Hi  
I want to calculate the density (head, tail, and water) from the center of my system. so I use this order:

gmx rdf -f micelle.gro -s md.tpr -o rdf.xvg -n index.ndx -ref 0 -sel 7  
(0 is the system group and 7 is my head group)  
after the calculation of Gromacs, you can see the g(r) on the y-axis but I want the number of density instead of that. i am completely confused what is the difference between g(r) and the number of density when we use RDF (when our y-axis is g(r) and when it is “number of density” and what do they mean ?)  
my ideal graph is attached.

 ![4](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/e/ea9502fb7b1156d2020d526a76e1485a26485343.png)  
Best regards,  
Shiva