What is IronXL and how can it be used in C# applications?

IronXL is a .NET Excel Library that helps developers create, read, and edit Excel files in C# applications. It is fast, accurate, and does not require Microsoft Excel to be installed, as it doesn't rely on Office Interop.

How do I convert an XLS file to an XLSX file using IronXL?

To convert an XLS to an XLSX file with IronXL, you use the 'SaveAs' method to save the file with a different file extension, making the conversion fast and straightforward.

Is Microsoft Excel required to use IronXL for Excel file manipulations?

No, IronXL does not need Microsoft Excel to be installed on the machine because it operates independently of Office Interop or any other dependencies.

What .NET versions are compatible with IronXL?

IronXL supports .NET 7, 6, and 5, .NET Core 2 and 3, as well as .NET Framework 4.5 and onwards, making it versatile for various C# projects.

Can IronXL handle different Excel file formats?

Yes, IronXL supports all Excel workbook file formats, including XLS, XLSX, XLSM, CSV, and TSV. It also allows data export to JSON, HTML, and other formats.

How does IronXL ensure data security in Excel files?

IronXL allows Excel files to be secured with user passwords and permissions, enhancing data security and control over who can edit the files.

Can IronXL edit and manage Excel cell data and layouts?

Yes, IronXL allows developers to edit formulas, sort data, and manage layouts by freezing panes, auto-sizing rows/columns, and adding/removing rows or columns.

What steps are needed to install IronXL in a C# project?

To install IronXL in a C# project, open 'Manage NuGet Packages for Solution,' search for IronXL, select your project, and click install. Include 'using IronXL;' in your code.

How can existing Excel files be loaded in IronXL?

Existing Excel files can be loaded in IronXL using the 'LoadExcel' method. This allows you to work with XLS, XLSX, XLSM, and other formats within your C# application.

Is there a free trial available for IronXL?

Yes, IronXL is free for development and offers a free trial for commercial use. It can be downloaded from the IronXL website.

The C# Excel Library

Explore IronXL Excel Spreadsheet Library for C# .NET Start Free Trial

Read Excel Files without Interop

See All Code Examples

using IronXL;
using System;
using System.Linq;

// Supported for XLSX, XLS, XLSM, XLTX, CSV and TSV
WorkBook workBook = WorkBook.Load("sample.xlsx");

// Select worksheet at index 0
WorkSheet workSheet = workBook.WorkSheets[0];

// Get any existing worksheet
WorkSheet firstSheet = workBook.DefaultWorkSheet;

// Select a cell and return the converted value
int cellValue = workSheet["A2"].IntValue;

// Read from ranges of cells elegantly.
foreach (var cell in workSheet["A2:A10"])
{
    Console.WriteLine("Cell {0} has value '{1}'", cell.AddressString, cell.Text);
}

// Calculate aggregate values such as Min, Max and Sum
decimal sum = workSheet["A2:A10"].Sum();

// Linq compatible
decimal max = workSheet["A2:A10"].Max(c => c.DecimalValue);

using IronXL;
using System;
using System.Linq;

// Supported for XLSX, XLS, XLSM, XLTX, CSV and TSV
WorkBook workBook = WorkBook.Load("sample.xlsx");

// Select worksheet at index 0
WorkSheet workSheet = workBook.WorkSheets[0];

// Get any existing worksheet
WorkSheet firstSheet = workBook.DefaultWorkSheet;

// Select a cell and return the converted value
int cellValue = workSheet["A2"].IntValue;

// Read from ranges of cells elegantly.
foreach (var cell in workSheet["A2:A10"])
{
    Console.WriteLine("Cell {0} has value '{1}'", cell.AddressString, cell.Text);
}

// Calculate aggregate values such as Min, Max and Sum
decimal sum = workSheet["A2:A10"].Sum();

// Linq compatible
decimal max = workSheet["A2:A10"].Max(c => c.DecimalValue);

PM >Install-Package IronXL.Excel

Install-Package IronXL.Excel

USING IRONXL

How to Convert XLS to XLSX File in C#

Curtis Chau

Updated: April 21, 2026

This article will explore the IronXL library to convert XLS to XLSX format in a C# Console Application.

IronXL - An Excel Library

IronXL is a .NET Excel Library that helps developers create, read, and edit Excel files in C# applications. It is fast and accurate regarding performance and output, respectively. It supports all Excel workbook file formats (XLS, XLSX, XLSM, CSV, TSV). IronXL also allows data to be saved or exported from Excel formats (XLS, XLSX) to JSON, HTML, Binary, Byte Array, DataSet, or DataTable.

IronXL allows developers to work with worksheets and cell ranges elegantly. With IronXL, you can edit formulas. Recalculation of the already given formula in the sheet is very easy to do. Data can be sorted based on range, column, or row. It provides you the facility to edit layouts like freeze panes, auto-size rows/columns, and add and remove rows/columns easily.

With IronXL, Excel files can be protected with a user password and permission to edit the file. Another feature is that you can add, remove, and extract images from Excel worksheets. It also provides a wide range of Excel functions with almost all cell data formats. This makes IronXL one of the most intuitive APIs when it comes to working with Excel files.

IronXL does not need Microsoft Excel to be installed on the machine as it does not require Office Interop or any other dependency. It works on multiple platforms and is compatible with .NET 7, 6 & 5. It also supports .NET Core 2 and 3 along with the standard 2 versions. .NET Framework 4.5 and onwards is also supported for working on Excel spreadsheets.

Create a Console Application

The latest version of Visual Studio is recommended for creating an application to start with. Visual Studio is the official IDE for C# development, and you must have it installed. You can download it from the Microsoft Visual Studio website if it's not already installed.

The following steps will create a new project named "DemoApp".

Open Visual Studio and click on "Create a New Project".

Open Visual Studio
Select "Console Application" and Click "Next".

Create a new project in Visual Studio
Set the name of the Project.

Configure your new project
Select the .NET version. Choose the stable version, .NET 6.0.

.NET Framework selection

Install IronXL Library

Once the project is created, the IronXL library needs to be installed in the project for use. Follow these steps to install it.

Open "Manage NuGet Packages for Solutions" either from Solution Explorer or Tools.

Navigate to NuGet Package Manager
Browse for the IronXL Library and select the current project. Click install.

Search and install the IronXL package in NuGet Package Manager UI

Add the following namespace at the top of the Program.cs file:

using IronXL;

using IronXL;

Imports IronXL

Imports IronXL

Open an Existing XLS file

IronXL provides the facility to open an existing Excel file, or you can create a new Excel file. Here we are going to open an existing Excel XLS file using the C# IronXL LoadExcel method. The Load method is a short synonym for LoadExcel.

// Load an existing Excel file. Supported formats include XLSX, XLS, XLSM, XLTX, CSV and TSV.
WorkBook workBook = WorkBook.LoadExcel("sample.xls");

// Load an existing Excel file. Supported formats include XLSX, XLS, XLSM, XLTX, CSV and TSV.
WorkBook workBook = WorkBook.LoadExcel("sample.xls");

' Load an existing Excel file. Supported formats include XLSX, XLS, XLSM, XLTX, CSV and TSV.
Dim workBook As WorkBook = WorkBook.LoadExcel("sample.xls")

' Load an existing Excel file. Supported formats include XLSX, XLS, XLSM, XLTX, CSV and TSV.
Dim workBook As WorkBook = WorkBook.LoadExcel("sample.xls")

The sample file loaded is as follows:

How to Convert XLS to XLSX File in C#, Figure 7: A sample XLS data file A sample XLS data file

To create Excel files in XLS or XLSX format, you can visit this code examples page here.

Convert XLS File to XLSX File

To convert an XLS to an XLSX file, IronXL just uses the SaveAs method to do this conversion. The following code shows how to save an XLS file to an XLSX file:

// Convert XLS to XLSX format by saving it with a different file extension.
workBook.SaveAs("converted_sample.xlsx");

// Convert XLS to XLSX format by saving it with a different file extension.
workBook.SaveAs("converted_sample.xlsx");

' Convert XLS to XLSX format by saving it with a different file extension.
workBook.SaveAs("converted_sample.xlsx")

' Convert XLS to XLSX format by saving it with a different file extension.
workBook.SaveAs("converted_sample.xlsx")

That's it. We have successfully converted an XLS to XLSX format. To convert to other formats, you can visit this code examples page.

Output

How to Convert XLS to XLSX File in C#, Figure 8: The exported XLSX file The exported XLSX file

You can see that the data is the same even after conversion. IronXL provides ease of use, speed, and accuracy.

Summary

This article demonstrated how to convert XLS Excel files to XLSX files using IronXL in C#. IronXL provides the facility to work with existing Excel files without any hassle. Conversion between different spreadsheet formats is usually a one-line process. It's fast, easy to use, and accurate. It also allows you to create new Excel files and write data to them with easy syntax. IronXL can also be used to read Excel files without Microsoft Office installed. To read data from Excel files, you can see this code example page.

IronXL is free for development and can be licensed for commercial use. You can also try IronXL for a free trial for commercial use. Download the software from the IronXL website.

Curtis Chau

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Technical Writer

Curtis Chau holds a Bachelor’s degree in Computer Science (Carleton University) and specializes in front-end development with expertise in Node.js, TypeScript, JavaScript, and React. Passionate about crafting intuitive and aesthetically pleasing user interfaces, Curtis enjoys working with modern frameworks and creating well-structured, visually appealing manuals.

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