---
title: "Create an Excel XLSX file in C#"
url: https://recursiveai.org/onedocument/cookbook/create-excel-file/
description: "Create an Excel XLSX file in C# with OneDocument for .NET 10. Free, open-source code with a runnable download, self-made inputs and real output."
version: "1.0.0"
---

# Create an Excel XLSX file in C#

**OneDocument** is a free, open-source Word, Excel and PowerPoint document library for .NET from Recursive AI. MIT or Apache-2.0, no native dependencies.

[NuGet](https://www.nuget.org/packages/RecursiveAI.OneDocument.Spreadsheets) · [GitHub](https://github.com/recursive-ai-oss/onedocument-csharp) · [Docs](https://recursiveai.org/onedocument/docs/)

```shell
dotnet add package \
    RecursiveAI.OneDocument.Spreadsheets
```

Requires .NET 10 (net10.0); .NET 9 and earlier aren’t supported.

```csharp
using RecursiveAI.OneDocument.Spreadsheets;
using var book = Workbook.Create();
book.Sheets[0]["A1"].SetString("Hello");
book.SaveAs("hello.xlsx");
```

Writes hello.xlsx with Hello in A1.

**[Download this example (.zip)](https://recursiveai.org/onedocument/cookbook/create-excel-file/create-excel-file.zip)**: unzip, then `dotnet run`.

## The full program

The download makes a budget workbook with two items, a SUM formula and currency formatting, then reopens it to read the saved total.

```csharp
using RecursiveAI.OneDocument.Spreadsheets;

using (Workbook made = Workbook.Create())
{
    Worksheet sheet = made.Sheets[0];
    sheet.Rename("Budget");
    sheet.Range("A1:B3").Values = new object?[,]
    {
        { "Item", "Cost" },
        { "Ladder", 189.5 },
        { "Bulbs", 42 }
    };
    sheet["A4"].SetString("Total");
    sheet["B4"].Formula = "SUM(B2:B3)";
    sheet.Range("B2:B4").NumberFormat = "$#,##0.00";
    made.Recalculate();
    made.SaveAs("budget.xlsx");
}

using Workbook check = Workbook.Open("budget.xlsx");
Console.WriteLine("Wrote budget.xlsx");
Console.WriteLine($"Budget total: {check.Sheets["Budget"]["B4"].FormattedText}");
```

`dotnet run` prints:

```text
Wrote budget.xlsx
Budget total: $231.50
```

A formula is not calculated just because it is assigned: this program explicitly calls `Recalculate` before saving. If the output directory does not exist, saving raises `DirectoryNotFoundException`; create it first.

## Variations

**Write a rectangular block of values.**

```csharp
using RecursiveAI.OneDocument.Spreadsheets;

using var book = Workbook.Create();
book.Sheets[0].Range("A1:B2").Values = new object?[,]
{
    { "Item", "Cost" },
    { "Bulbs", 42 }
};
book.SaveAs("items.xlsx");
```

Writes items.xlsx with a header and one data row.

## Related recipes

- [Convert DOCX to PDF in C#](https://recursiveai.org/onedocument/cookbook/convert-docx-to-pdf/)
- [Read an Excel file in C#](https://recursiveai.org/onedocument/cookbook/read-excel-file/)
- [Read a Word DOCX document in C#](https://recursiveai.org/onedocument/cookbook/read-word-document/)
- [Convert Excel to PDF in C#](https://recursiveai.org/onedocument/cookbook/convert-excel-to-pdf/)

---

## The short answer

To create an Excel XLSX file in C#, install OneDocument’s Spreadsheets package, call `Workbook.Create`, write values into its first worksheet, and call `SaveAs` with an `.xlsx` path. The snippet at the top creates hello.xlsx with one text cell. The download shows the next useful step: a small budget with data, formatting and a formula whose result is saved in the file.

Keep creation, calculation and saving separate in your code. They do different jobs. Writing a value edits the workbook model; assigning a formula stores the expression; `Recalculate` computes results; `SaveAs` writes the output file. That separation makes it clear whether the workbook you hand to another program contains current calculated results.

## How can I create an Excel spreadsheet using C#?

A new workbook already has a worksheet. Use `Sheets[0]` to get it, then `Rename` if your output needs a stable name. The full example calls it Budget. Address individual cells with A1 coordinates, or assign a rectangular `object?[,]` array to a matching range. The array’s rows and columns correspond to the target rectangle; the variation demonstrates a header and one data row.

Use `SetString` for text and numeric values for amounts you want to calculate. A string that looks like a currency value is still text. In this example, 189.5 and 42 are numbers; the dollar sign comes from the cell’s number format. The [spreadsheet documentation](https://recursiveai.org/onedocument/docs/spreadsheets/) explains the value kinds and how cell values are stored.

Saving is explicit. `SaveAs` writes the file; `using` only frees memory. Keep the generated file’s path available to the next step in your application, whether that step is downloading the workbook, reading it back, or converting it to a printable report.

## Can I create an Excel file in C# without installing Excel?

Yes. This code writes the workbook through OneDocument, not through Excel automation. The package is a .NET 10 library with no native dependencies. The downloadable project references the published 1.0.0 package and makes all its own data; no desktop application or template file is part of the example.

Use the `.xlsx` extension for this output. Do not turn a CSV into an XLSX by renaming it: writing a workbook means producing its workbook and worksheet structure, not just comma-separated text. OneDocument’s save path selects the output format. If you want another supported format, choose it deliberately and check what that format can represent.

## How do I add formulas to an Excel file in C#?

The full program assigns `SUM(B2:B3)` to B4, without a leading equals sign, then calls `Recalculate`. It applies `$#,##0.00` to B2:B4 so that the two amounts and total display consistently. Reopening the saved file returns `$231.50` for the total, which is the result of this sample’s two numeric inputs.

Calculation and formatting are independent. A number format changes how a value is shown, not the number that SUM uses. Similarly, storing a formula is not the same as running the calculation engine. Recalculate before exporting the workbook to a format that reads cached results, such as PDF.

There is also a language constraint: the [README](https://recursiveai.org/onedocument/docs/overview/) states, “Formula text is en-US and invariant only; localized function names are not supported.” Write formulas using the documented invariant syntax, even if the person opening the workbook uses a localized Excel interface. Test the particular functions your workbook needs instead of assuming that every possible Excel formula is interchangeable.