For calculating single tile size from image dimensions and number of rows and columns specified and for calculating number of rows and columns from tile size and image dimensions.
Equation for calculating tilesize:
Width: Sheet width / columns.
Height: Sheet height / rows.
Equation for calculating number of rows/columns:
Columns: Sheet width / tile width
Rows: Sheet height / tile height
I understand that options that are already there should stay as spritesheet can be sometimes more complicated. But if all you need is to decompose tileset and you want all tiles while only know tilesize or numbers of rows and columns, such buttons would make things MUCH easier.