Although I didn't find any international standard, it appears most soap bars weigh 4 oz, which is Yankee for 113.4 grams. However, my research was stopped by this graphic of Pacific oceanic currents. The downward trajectory of that soap bar isn't going to be vertical at all; an additional question could be: where in the Pacific should you drop your soap bar for the currents to take it to the Mariana Trench?