Highlight 6 columns, then do your Insert to insert 6 more columns (or
Rows) etc ...

Bryan, thank you. I was looking for something like that. But I would
still like to control the number of rows in another way. Because in my
work I actually have to insert 237 rows every now and then and I would
like to avoid troublesome arithmetic. So it might be nice if excel had
an insert menu with before e.g. rows a textbox with by default the
number 1 but that could be changed by the user.

To avoid troublesome arithmetic, you might:
- select rows 1 to 237 (starting at 237 and dragging up to 1)
- use Bryan's method to insert rows at the top of the sheet
- select the new empty rows, and use "cut/insert cut cells" to move
them where you want.