By default 14 is the period for the RSI indicator. So it is calculated on a 14-period basis. But we can play with the settings. I have seen 7-period is a good period to use in intraday. It can also be used for positional trading apart from intraday, as it gives the overbought oversold signals faster. There is a much faster setting used by Larry Connors. He used a 2--period version of this indicator to build a highly profitable trading system.