Skip to main content

How to convert column index into letters with Google Apps Script

Although Google Sheets does not provide a ready-to-use function that takes a column index as an input and returns corresponding letters as output, we can still do the task by leveraging other built-in functions ADDRESS, REGEXEXTRACT, INDEX, SPLIT as shown in the post. However, in form of a formula, that solution is not applicable for scripting with Google Apps Script. In this post, we look at how to write a utility function with Google Apps Script that converts column index into corresponding letters.

With the solution in the form of a formula, we don't even need to understand how column index and letters map each other. With apps script, we need to understand the mapping to come up with an algorithm.

In a spreadsheet, columns are indexed alphabetically, starting from A.

  • Obviously, the first 26 columns correspond to 26 alphabet characters, A to Z.
  • The next 676 columns (26*26), from 27th to 702nd, are indexed with 2 letters. [AA, AB, ... AY, AZ], [BA, BB, ... BY, BZ], ... [MA, MB, ... MY, MZ], ... [ZA, ZB, ... ZY, ZZ]. Each alphabet character takes a turn (in order) to precede all 26 alphabet characters.
  • The next 17576 columns (26*26*26), from 703rd to 18278th, are indexed with 3 letters. [AAA, AAB, ... AAY, AAZ], [ABA, ABB, ... ABY, ABZ], ... [ZZA, ZZB, ... ZZY, ZZZ]. Each letter AA to ZZ above takes a turn (in order) to precede all 26 alphabet characters.
  • etc.

The above observation suggests a recursive pattern. Columns with 3 letters depend on columns with 2 letters, columns with 2 letters depend on columns with 1 letter. Moreover, the number of letters for a column depends on its index divided by 26. It suggests that we need to divide column index by 26 to apply the recursive pattern. So, here are the steps of the algorithm:

  • let ALPHABETS=['A', 'B', 'C', 'D', ... 'X', 'Y', 'Z']
  • if k <= 26, then return ALPHABETS[k - 1];
  • else return getColumnLetters(k / 26) + ALPHABETS[(k % 26) - 1]
Column IndexColumn LettersDivide by 26

Let's take the column 1963rd as an example:

  • As 1963=75*26+13, the 1963rd column letters are the concatenation of the 75th column letters and the 13th column letters.
    • As 13 < 26, the 13rd column's letter is the 13rd alphabet character that is M.
    • As 75 = 2 * 26 + 23, the 75th column letters are the concatenation of the 2nd column letters and the 23rd column letters.
      • As 2 < 26, the 2nd column letter is the 2nd alphabet character that is B.
      • As 23 < 26, the 23rd column letter is the 23rd alphabet character that is W.
      • The 75th column letters are hence B + W = BW.
    • The 1963rd column letters are hence BW + M = BWM.

Let's analyze the column 988th that is a little bit trickier because 988 is divisible by 26:

  • As 988=38*26+0, the 988th column letters are the concatenation of the 38th column letters and the 0th column letters. But wait, column index starts from 1, doesn't it?.
    • In fact, as 988 is divisible by 26, it can be expressed as 988=37*26+26. That means the 988th column letters are the concatenation of the 37th column letters and the 26th column letters.
    • As 26 = 26, the 26th column letter is the 26th alphabet character that is Z.
    • As 37 = 1 * 26 + 11, the 37th column letters are the concatenation of the 1st column's letter and the 11th column's letter.
      • Because, 1 < 26, the 1st column letter is the 1st alphabet character that is A.
      • As 11 < 26, the 11th column letter is the 11th alphabet character that is K.
      • The 37th column letters are hence A + K = AK.
    • The 988th column letters are hence AK + Z = AKZ.

To implement this algorithm in javascript, we need to pay attention to certain points:

  • The column index, which is the input of the function, starts from 1, while the array in javascript starts from 0.
  • When dividing the column index by 26, we need to round the result down.
  • If the column index is divisible by 26, the residual is 0. To apply the next recursive call, we need to reduce the result by one while increasing the residual by 26.

Finally, you can find below an example of code to convert column index into corresponding letters in Google Apps Script and a test function that prints out letters for all the first 1000 columns in 3 different ways that we have discovered in these 2 posts.

function getColumnLetters(columnIndexStartFromOne) { const ALPHABETS = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'] if (columnIndexStartFromOne < 27) { return ALPHABETS[columnIndexStartFromOne - 1] } else { var res = columnIndexStartFromOne % 26 var div = Math.floor(columnIndexStartFromOne / 26) if (res === 0) { div = div - 1 res = 26 } return getColumnLetters(div) + ALPHABETS[res - 1] } } function test() { var rows = [] var row1 = [] var row2 = [] var row3 = [] var row4 = [] for(let i = 1; i < 1000; i++) { row1.push(getColumnLetters(i)) row2.push(i) row3.push('=REGEXEXTRACT(ADDRESS(1, ' + i + '),"\\$([A-Za-z]+)\\$")') row4.push('=INDEX(SPLIT(ADDRESS(1, ' + i + '),"$"),1,1)') } rows.push(row1, row2, row3, row4) var sheetName = "test" var spreadsheet = SpreadsheetApp.getActive() var sheet = spreadsheet.getSheetByName(sheetName) if (sheet) { sheet.clear() } else { sheet = spreadsheet.insertSheet(sheetName, spreadsheet.getNumSheets()) } sheet.getRange(1, 1, rows.length, rows[0].length).setValues(rows) }


  1. Hello Friend, I found this and I think is better:

    function columnToLetter(column)
    var temp, letter = '';
    while (column > 0)
    temp = (column - 1) % 26;
    letter = String.fromCharCode(temp + 65) + letter;
    column = (column - temp - 1) / 26;
    return letter;

    1. Hi,

      Nice way of using while loop instead of recursive programming.

      Thanks for your comment.


Post a Comment

People also enjoyed…

Create personal stock portfolio tracker with Google Sheets and Google Data Studio

I have been investing in the stock market for a while. I was looking for a software tool that could help me better manage my portfolio, but, could not find one that satisfied my needs. One day, I discovered that the Google Sheets application has a built-in function called GOOGLEFINANCE which fetches current or historical prices of stocks into spreadsheets. So I thought it is totally possible to build my own personal portfolio tracker with Google Sheets. I can register my transactions in a sheet and use the pivot table, built-in functions such as GOOGLEFINANCE, and Apps Script to automate the computation for daily evolutions of my portfolio as well as the current position for each stock in my portfolio. I then drew some sort of charts within the spreadsheet to have some visual ideas of my portfolio. However, I quickly found it inconvenient to have the charts overlapped the table and to switch back and forth among sheets in the spreadsheet. That's when I came to know the existen

Create a dividend income tracker with Google Sheets by simply using pivot tables

As my investment strategy is to buy stocks that pay regular and stable dividends during a long-term period, I need to monitor my dividends income by stocks, by months, and by years, so that I can answer quickly and exactly the following questions: How much dividend did I receive on a given month and a given year? How much dividend did I receive for a given stock in a given year? Have a given stock's annual dividend per share kept increasing gradually over years? Have a given stock's annual dividend yield been stable over years? In this post, I explain how to create a dividend tracker with Google Sheets. Manage stock transactions with Google Sheets Create dividend tracker with Google Sheets Track annual dividend amount of stocks Track dividend amount by month and by year Track annual dividend per share of stocks Track annual dividend yield of stocks Demo Conclusion References Manage stock transactions with Google Sheets I use a spreadsheet on Goo

How to copy data in Google Sheets as HTML table

I often need to extract some sample data in Google Sheets and present it in my blog as an HTML table. However, when copying a selected range in Google Sheets and paste it outside the Google Sheets, I only get plain text. In this post, I explain how to copy data in Google Sheets as an HTML table by writing a small Apps Script program. Concept Implementation Source Code Demo HTML table code HTML table visualization Getting Started Conclusion Concept On a spreadsheet, users select a range that they want to copy as HTML table. With the selected range, users trigger a command Copy AS HTML table . The command can be added to the toolbar, or to the contextual menu, or accessed via a keyboard shortcut. The command is executed to transform the selected range into HTML code for table. The HTML code can be added to the clipboard or can be displayed somewhere so users can copy it manually. The HTML table must consist of all displayed cells of the selected range and the widths