End to end polymer distance calculation

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How to calculate end to end distance for a polymer system?
(I am not an expert in Gromacs and in the learning stage.)

I have a polymer (10 mer) and created a melt system with 50 individual chains. ~ 5500 atoms. I completed production run, and want to find the end-to-end distance (chain length) of an individual polymer chain. Could anyone help me with the procedure towards end-to-end distance calculation.
(Confused about the flow chart of procedure - do I need to generate index file, should I use gmx distance, gmx mindist or gmx pairdist?)

Thank you for your interest and response.

Kind Regards

you can generate an index file and the use gmx distance. This post may help you

In general for the difference between

you can look to the following post

Best regards