In the framework of the project EXTREMEVENT, we measured the topographic and granulometric attributes of coastal boulders in various places in the Noth Atlantic : the coasts of the Reykjanes Peninsula (southwestern Iceland), the coasts of Brittany (western France). This dataset gathers these attributes as follow:- the date, the country, the region, and a site identifier;- the type of boulder (CTB = cliff-top boulder; SPB = supratidal platform boulder);- the X, Y and Z positions, measured with a differential global positioning system (DGPS) in real-time kinematic (RTK) mode (initially measured in a local coordinate reference system (EPSG:5326 in Iceland, EPSG:2154 in France) and then converted to EPSG:4326; altitudes are given in meters above mean sea level);- the length of the A (longest axis), B (intermediate axis) and C (shortest axis) axes of the boulders, measured with a measuring tape;- the inland distance, corresponding to the distance of each boulder's location from the nearest position of the highest astronomical tide level;- the density of the rock in which the boulders are made.