Scientists seem to have found the answer to a question that has troubled them for a long time.

Scientists say that the answer lies in the height of the table. The experiment revealed that after the toast is dropped, it falls off the edge and has time just enough to perform a half somersault before it lands.
Since the side that has been buttered is naturally facing upwards, that’s the side which actually lands on the floor.
‘The upshot is that if you want to ensure your toast lands butter side up then you should invest in a higher table approximately 8ft high that allows the toast to rotate a full 360 degrees,’ researchers said.
Source-Medindia