Within MS Excel one can adjust the height of a row by dragging the boundary below the row heading until the row is the wanted height or double-click the boundary to get an automatically adjusted height that fits the content.

This is true for single column, non-merged cells, whereas the first method also applies to merged cells. But imagine a 300 row sheet. I would not want to drag every row to a certain height after changing the font size. One could say: “Alright, I’ll just select the whole sheet by clicking the field left to A and above 1, drag one row to a height that fits the maximum height.” Lots of empty spaces. Does not look good.

Anyway, in writing the document just add a simple step.

wrapped text in merged cell after auto adjusting the height

In ‘Format Cells… (right click to cell) – Alignment’ select ‘Wrap Text’ while ‘Merge cells’ should be already selected.
Then in a single column cell enter manual line breaks (Alt+Enter while in edit mode). Adapt the number of line breaks to the number of lines in the merged cell, hit Enter and there you are.

wrapped text in merged cell after auto adjusting the height with applied manual line break in B14

Dat’s dat. Yo ho!