Column Letter Converter
Convert Excel column letters to numbers and back
Column Letter Converter tool
Max: XFD (16384)
Common Conversions
- • A ↔ 1
- • Z ↔ 26
- • AA ↔ 27
- • AB ↔ 28
- • AZ ↔ 52
- • BA ↔ 53
- • XFD ↔ 16384
Column Letter Converter: key facts
- What it does
- Convert Excel column letters to numbers and back
- Category
- Workplace Tools
- Cost
- Free, with no account, sign-up, or install.
- Your data
- Runs entirely in your browser — the files and text you enter are never uploaded to a server.
- Last reviewed
- . Report an incorrect result.
What the Column Letter Converter does
Every column in Excel and Google Sheets has two identities: the letter label you see in the spreadsheet header (A, B, Z, AA, XFD) and the underlying integer index used in formulas, scripts, and APIs (1, 2, 26, 27, 16384). The letter system feels natural when you are clicking around a spreadsheet, but the moment you write a formula that calculates a column address dynamically — using OFFSET, INDEX, or a VBA loop — you need to work in numbers and convert back to letters for display or reference.
Excel supports up to 16,384 columns per sheet, spanning from A to XFD. The encoding is a base-26 variant where A=1 (not 0), which means the rollover points differ slightly from pure base-26: Z is 26, AA is 27, AZ is 52, BA is 53. This converter handles the full range with the correct algorithm, validates inputs against the XFD limit, and returns an error message instead of a silent wrong result if you exceed the maximum.
Using the Column Letter Converter, step by step
- Choose the direction: "Letter → Number" to convert a column label like AA to its index, or "Number → Letter" to find the letter for a column index.
- Type the column letter (e.g., AB) or column number (e.g., 28) into the input field.
- The converted value appears immediately in the output field. An error message shows if the input is invalid or exceeds the Excel column limit (XFD / 16384).
- Click "Copy Result" to copy the answer to your clipboard for pasting into a formula or script.
Base-26, but not quite
Spreadsheet column labels look like base-26 and are not, because there is no zero digit. A is 1 rather than 0, so after Z the next label is AA rather than a two-digit form containing a zero. The system is properly called bijective base-26, and it is why the conversion needs care rather than a straight radix change.
The consequence is that AA is 27, not 26 as a naive reading would give. Each additional letter position multiplies by 26 and the offsets compound, so the arithmetic has to account for the missing zero at every step.
Conversion runs both ways: letter to number for working out how far across a column sits, and number to letter for turning a computed index into something you can type.
- A is 1, Z is 26, AA is 27, and AZ is 52.
- BA is 53 — the second cycle beginning again.
- Excel's last column is XFD, which is 16,384.
What makes this one worth using
- Full Excel range support: the converter covers the complete column space from A (1) through XFD (16384), validating that your input does not exceed the Excel hard limit before returning a result.
- Correct base-26 arithmetic: column letters do not follow pure base-26 (where A would be 0). They use a 1-indexed variant where A=1, Z=26, AA=27. The converter implements this exactly, so edge cases like Z, AA, and AZ produce the right numbers.
- Error feedback: invalid letters and out-of-range numbers produce a clear error message rather than silently returning a wrong value, so you know immediately when your input is outside the valid range.
- Instant results: conversion happens as you type with no button press required, making it fast to check multiple columns in succession.
Where the conversion is actually needed
The common case is bridging code and interface. Spreadsheet libraries and APIs generally address columns by number while the file and the user talk in letters, so any script that reads or writes a specific column ends up needing this conversion. Getting it wrong by one — the classic off-by-one from treating A as zero — writes data into the wrong column, which is the kind of bug that is discovered late.
It also comes up in reverse when diagnosing. An error or a log entry citing column 741 is meaningless until you know it means ABM, and finding that by counting across a spreadsheet is not practical.
Two practical notes. The same bijective scheme appears elsewhere — in some spreadsheet-like tools and in a few identifier schemes — so the arithmetic transfers. And where a column position is genuinely important to your logic, referring to it by a named range or a header lookup rather than a fixed letter or index is more robust, since inserting a column shifts every position after it while leaving names intact.
Frequently Asked Questions
Why does AA equal 27 instead of 27 in regular base-26?
In regular base-26 with A=0, Z would be 25 and AA would be 26. But Excel's column letters use A=1 (1-indexed), which shifts every value up by 1. This is why Z=26, AA=27, AZ=52, and BA=53. The converter implements this 1-indexed variant exactly.
What is column XFD and why is it the limit?
XFD is column 16,384, which is 2^14. Microsoft chose 16,384 columns as the limit in the Excel 2007 specification (XLSX format) and Google Sheets adopted the same limit. Earlier versions of Excel had only 256 columns (IV). The converter will refuse any letter beyond XFD or any number above 16384.
How do I use column numbers in Excel formulas?
The COLUMN() function returns the column number of any cell reference. OFFSET() accepts a column count as its third argument. INDEX() takes a column number in its third argument. MATCH() returns a position number you can feed into INDEX. If you need the letter from a number in a formula, =SUBSTITUTE(ADDRESS(1,n,4),1,"") extracts just the letter from a constructed address.
