I Confidence interval on Standard deviation

[iVenky]

I read that confidence interval on standard deviation can be found using chi-square distribution. If I have a sample size N=500, and sample standard deviation= 3 with mean=0, and I need a 95% confidence, I wasn't sure what to set for degrees of freedom in chi-square formula. Is the degrees of freedom same as the sample size? Is there an online-tool that can do the math for you if I enter the values?

 

[.Scott]

You can calculate your confidence interval with this tool:
Confidence Interval

The degrees of freedom is you sample size minus one (499), but that is not required by this tool.

 

[iVenky]

Hi,

Thanks for the reply, but I am interested in confidence interval of the standard deviation rather than the mean. The link that you mentioned doesn't contain the confidence interval for standard deviation

 

[.Scott]

Here is a tool: CI of SD Tools
That tools reports: 2.82 to 3.20

The site below provides a more specific example in one of its tables:
https://www.graphpad.com/guides/prism/7/statistics/stat_confidence_interval_of_a_stand.htm
For the 95% Confidence Interval of the SD and n=500, it reports: 0.94*SD to 1.07*SD

And the degrees of freedom is still 499.

 

[iVenky]

Thank you very much!