An OPC feature measurement technique accurately measures serif area of OPC features, feature separation and line symmetry, and is especially useful for measuring dimensions which are less than about the wavelength of the examining radiation. The relative area of serifs present on a line end is measured by first defining a region of interest around the line end and then an intensity profile is created. The differences between data points on the profile and a constant value are summed in order to calculate a flux value. The flux value is divided by the intensity range to determine an area. The separation distance between a line end and another feature is determined by first defining a region of interest that spans the separation distance between the two features. Next, an intensity profile is created. The differences between data points on the profile and a constant value are summed to calculate a flux value. The separation distance between the features is calculated from the flux value. The asymmetry of serifs of a line present on a photomask is determined by first defining two regions of interest: a shank region of interest that includes the shank of the line and an end region of interest that includes the end of the line. Intensity profiles are created for both regions of interest. The profiles are created by summing values in a longitudinal direction with respect to the line. Finally, an asymmetry area value for the serifs is calculated using the end intensity profile and a centroid of the shank region of interest. The effective diameter, the separation distance and the asymmetry area are useful for evaluating the quality of the photomask.