---
url: /process-functions/workbook-columnnametoindex.md
description: Returns a column's index from its letter.
---

# workbook.columnNameToIndex

Returns a column's index from its letter, starting at `0`. For example, `"A"` returns `0` and `"AA"` returns `26`. Throws an error if the name isn't a valid column letter.

```js
workbook.columnNameToIndex(columnName)
```

## Parameters

| Parameter | Type | Description |
|---|---|---|
| `columnName` | `string` | The column's letter, such as `"BC"`. Not case-sensitive. |

## Returns

The column's index.

## Examples

```js
const index = workbook.columnNameToIndex("AB"); // 27
```

## Related

* [workbook.columnIndexToName](/process-functions/workbook-columnindextoname)
* [ExcelWorkbook](/process-functions/excel-workbook)