I was looking for a good way to convert a number to the Excel column letter, for example:

1 -> A

26 -> Z

27 -> AA

28 -> AB

800 -> ADT

etc.

After searching on Google, I could not find any algorithm I want. (The closest one can handle up to two letters, i.e., ZZ. It will crash if the number is too large.). So I ended up creating my own.

Basically, you can think of this problem as a 26 based number conversion. Here is the php version. It should be pretty simple to convert it to a different language. Let me know if you have any problem.

function columnLetter($c){ $c = intval($c); if ($c < = 0) return ''; $letter = ''; while($c != 0){ $p = ($c - 1) % 26; $c = intval(($c - $p) / 26); $letter = chr(65 + $p) . $letter; } return $letter; }

Usage: columnLetter(1303618093); //DERRICK

Note that if you prefer lower cases rather than upper cases, you can simply replace 65 by 96 in the code.

Enjoy~!

–Derrick

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Thank you!

Thank you so much !! At least THE real algo than can handle more than 2 letters 🙂

I’ve tried to find it by my own, but i failed. Not a real 26 based number in fact, as the “0” digit is skeeped.

Thanks you!

Simple and effective!

Here goes an inverse function of this to convert back from a column letter to a number.

Supports up to 3 letters to col ‘ZZZ’.

function column_number($col){

$col = str_pad($col,3,’0′,STR_PAD_LEFT);

$i = 0;

if ($col{0} != ‘0’) {

$i = ((ord($col{0}) – 64) * 676)+26;

$i += ($col{1} == ‘0’) ? 0 : (ord($col{1}) – 65) * 26;

} else {

$i += ($col{1} == ‘0’) ? 0 : (ord($col{1}) – 64) * 26;

}

$i += ord($col{2}) – 64;

return $i;

}

Based off http://www.bradino.com/php/excel-column-convert-letters-to-numbers/#comment-427148

Undefined variable: letter

Last line of “while” loop… $letter = chr(65 + $p) . $letter;

Last $letter is not defined.

Fixed.

Thanks!