Column Letter Converter

Letters, Numbers, and Why AA Is 27

Excel numbers its columns in bijective base 26: twenty-six digits, A through Z, and no zero. A is 1, Z is 26, and because there is no digit for nothing, the next column has to add a place - AA is 27, not 26. Every awkward boundary follows from that missing zero, which is why counting letters by hand goes wrong around Z, AZ, and ZZ. The converter accepts either direction: type letters and get the number, type a number and get the letters. Input is trimmed and case-insensitive, and anything outside 1 to 16,384 is rejected rather than wrapped around.

A worksheet is 16,384 columns by 1,048,576 rows, and both limits are enforced here: XFE and row 1,048,577 come back as out of range, which is a quick way to check whether a generated reference is actually addressable before you paste it into a formula.

Expanding a Range Into Cells

Give the expander two full references - A1:C3 - and it lists every cell between them, reading left to right then down: A1, B1, C1, A2, and so on. It also reports the shape, so A1:C3 reports 3 rows x 3 columns = 9 cells. References in either order work, since the corners are normalized before expanding, and sheet prefixes and dollar signs are accepted and ignored for this purpose. The output list is bare references, joined by commas or one per line, ready to paste into a formula argument, a script, or a test fixture. Two limits: whole-column and whole-row forms such as A:A and 1:1 cannot be expanded because they have no bounds to enumerate, and the visible list stops at 1,000 cells while the reported total stays exact.

A1 and R1C1

R1C1 addresses a cell by row and column number instead of a letter and a number, and it distinguishes absolute from relative by notation rather than by dollar signs. A plain number is absolute - R1C1 is $A$1 wherever it appears. A number in square brackets is an offset from the current cell, so R[-1]C[2] means one row up and two columns right, and an omitted bracket means no movement in that direction: RC[-1] is the cell immediately to the left. Set the anchor cell to the cell the formula lives in, and the two boxes convert in both directions against it.

This is the notation macros use, and it is worth reading fluently for one reason: in R1C1, a relative formula copied down a hundred rows has the same text in every row. That makes it obvious at a glance whether a column of formulas is consistent - the thing A1 notation actively hides.

When a Different Tool Fits Better

If you have the column number in a cell and want the reference to be live, the INDIRECT generator builds it from a number, and the OFFSET generator moves a given number of rows and columns from an anchor without any letters at all. Better still, avoid column letters in lookups entirely with INDEX and MATCH, which addresses by position and survives inserted columns. To understand a reference you have inherited rather than build one, paste it into the formula explainer, and when you want to actually keep, drop, or reorder those columns in a file, use Excel Column Extractor.