Methods and apparatus to determine impression corresponding to market segments are disclosed. An example method includes determining a number of impressions that occurred on mobile devices and that are attributable to a first demographic group, where the number of impressions are based on attributions of the impressions to the first demographic group. The example method also includes determining whether a size of a first audience that corresponds to the first demographic group satisfies a threshold, where the first audience includes panelists in an audience measurement panel. The example method further includes determining whether a size of a second audience satisfies the threshold when the size of the first audience does not satisfy the threshold, where the second audience includes panelists in the audience measurement panel that correspond to a second demographic group and the first audience is a subset of the second audience. The method further includes calculating impressions attributable to a market segment and to the second demographic group when the second size of the second audience satisfies the threshold based on a portion of the second audience that belongs to the market segment.