The first example divides the screen vertically in two (i.e., creates a top half and a bottom half).
<FRAMESET rows="50%, 50%"> ...the rest of the definition... </FRAMESET>
The next example creates three columns: the second has a fixed width of 250 pixels (useful, for example, to hold an image with a known size). The first receives 25% of the remaining space and the third 75% of the remaining space.
<FRAMESET cols="1*,250,3*"> ...the rest of the definition... </FRAMESET>
The next example creates a 2x3 grid of subspaces.
<FRAMESET rows="30%,70%" cols="33%,34%,33%"> ...the rest of the definition... </FRAMESET>This info provided by W3C