This page allows to conveniently determine the name of an OSM tile as computed by the OSM user Computerteddy. Use left mouse click on the map to choose the top left tile and right mouse click to choose the bottom right tile. The chosen area will be colored blue. The top left and bottom right tile numbers will be displayed below the map as will a sendmap command which can be used to compute a Garmin map from the colored tiles.
Please note that the script currently will not work properly if you select an area that crosses the 180° longitude (e.g. from longitude 179 to -179).