The average directional index (ADX) is a trend indicator that is used to measure the strength of a current trend. The indicator is seldom used to identify the direction of the current trend, but can identify the momentum behind trends.
The ADX is a combination of two price movement measures: the positive directional indicator (+DI) and the negative directional indicator (-DI). The ADX measures the strength of a trend but not the direction. The +DI measures the strength of the upward trend while the -DI measures the strength of the downward trend. These two measures are also plotted along with the ADX line. Measured on a scale between zero and 100, readings below 20 signal a weak trend while readings above 40 signal a strong trend
An indicator used in technical analysis as an objective value for the strength of trend. ADX is non-directional so it will quantify a trend's strength regardless of whether it is up or down. ADX is usually plotted in a chart window along with two lines known as the DMI (Directional Movement Indicators). ADX is derived from the relationship of the DMI lines.