Abstract: Described is a technology in which a user interface element (a control, e.g., a datagrid) provides smoother scrolling by computing and updating a row height estimate. For example, the row height estimate along with the total number of rows may be used to configure a scrollbar. A control outputs visible rows according to user scrolling interaction based on a current row index and current pixel values corresponding to that current row index. The estimate is obtained based upon the current row index and the current pixel value for the row index. Whenever a row index is encountered that is larger than any previously-encountered row index, the row height estimate is updated, e.g., to reconfigure the scrollbar. Also described is outputting partially visible rows based on a number of pixels available in a display area below a last fully visible row, and/or above a first fully visible row.