If the formula already exists in a cell you can fill it down as follows:
- Select the cell containing the formula and press CTRL+SHIFT+DOWN to select the rest of the column (CTRL+SHIFT+END to select up to the last row where there is data)
- Fill down by pressing CTRL+D
- Use CTRL+UP to return up
On Mac, use CMD instead of CTRL.
An alternative if the formula is in the first cell of a column:
- Select the entire column by clicking the column header or selecting any cell in the column and pressing CTRL+SPACE
- Fill down by pressing CTRL+D