How do you copy a formula down a column with the org-mode spreadsheet

My personal preference is to add a column formula directly into the cell, instead of having to remember so many keyboard shortcuts.

Just start typing into the cell, starting with a = sign. For example, in column 3 type =$1+$2 and that formula will apply to all of the column directly.

You need to C-c C-c to actually apply the formula and calculate results.

For a single cell (non-column) formula, start with := instead.

What you are looking for is to use C-3 C-c = where 3 is the number of rows you want the formula to apply to.

| 3 | 4 |   |
| 2 | 8 |   |

If I C-2 C-c = in the column after the 4. I can input my formula of $1+$2 which will cascade down to each row, giving me the result of

| 4 | 3 |  7 |
| 2 | 8 | 10 |
#+TBLFM: $3=$1+$2

You are also free to just add #+TBLFM: $3=$1+$2 to the bottom of your table. You can force the formula to revaluate its values with C-c C-c when your point is anywhere over the formula.

C-u C-c C-c re-applies all formulas.

For example, given

| 3 |  4 | _ |
| 2 |  8 |   |
| 1 | 12 |   |

(where _ marks the location of the cursor) you could type C-c =¹, then enter a formula such as

$3=$1+$2

So the table looks like:

| 3 |  4 | 7 |
| 2 |  8 |   |
| 1 | 12 |   |
#+TBLFM: $3=$1+$2

Now typing C-u C-c C-c yields

| 3 |  4 |  7 |
| 2 |  8 | 10 |
| 1 | 12 | 13 |

¹Alternatively, use C-c ' to open a formula editing buffer, write and/or edit the formulas, then close the buffer (with C-x C-s) instead. I find this more convenient since you can use all emacs commands in the buffer, instead of just the limited set you can use in the minibuffer.