Relative strength is the relative comparison between two securities that lets one to identify the level of relative performance. It is calculated by dividing the price of one security with that of the other. Typically, the numerator consists of the security whose performance you want to gauge relative to that of the other. For instance, if you want to see how HDFC Bank is performing relative to Nifty, you would include HDFC Bank in the numerator and Nifty in the denominator.
To learn more about relative strength, click here77
Meanwhile, Relative Strength Index (or RSI) is a momentum indicator specific to just one security. The RSI measures the strength or the momentum of the price trend by comparing average gains with average losses over the past 'n' periods.
To learn more about the RSI, click here14
By the way, did you know that the RSI can be plotted on a Relative Strength chart as well?