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Download Excel File in ASP .NET C#: Export Data to XLSX, CSV & More

Jordi Bardia
Jordi Bardia
Published:

Implementing spreadsheet export functionality is a common requirement for enterprise web applications, yet the manual process of generating and delivering these files often introduces significant technical complexity. Developers must frequently navigate the nuances of MemoryStream management and configure precise HTTP content-disposition headers to ensure consistent browser behavior and prevent data corruption.

This article walks through everything needed to create and download Excel file in ASP .NET C# MVC controllers using the IronXL library. We'll cover exporting data to real Excel files in XLSX format, streaming CSV files, converting uploads for re-export, and returning file downloads to the browser, all without installing Microsoft Office or relying on Excel Interop. Install the IronXL NuGet package and start a free trial to follow along with the source code examples.

NuGet Install with NuGet

PM >  Install-Package IronXL.Excel

Check out IronXL on NuGet for quick installation. With over 10 million downloads, it’s transforming PDF development with C#. You can also download the DLL.

How to Create and Download an Excel File from a Controller?

The core pattern for any download excel file in ASP.NET Core scenario involves three steps: create the workbook, write it to a stream, and return the stream as a file response. The following code shows a complete MVC controller action that builds an XLSX file from scratch and pushes it to the browser.

using IronXL;
using Microsoft.AspNetCore.Mvc;
public class ReportController : Controller
{
    // Export employee data as a downloadable Excel file
    public IActionResult DownloadExcel()
    {
        // Create a new workbook and worksheet
        var workbook = WorkBook.Create(ExcelFileFormat.XLSX);
        var worksheet = workbook.CreateWorkSheet("Employees");
        // Add header row with column names
        worksheet["A1"].Value = "Name";
        worksheet["B1"].Value = "Department";
        worksheet["C1"].Value = "Salary";
        // Populate cells with data values
        worksheet["A2"].Value = "Alice Torres";
        worksheet["B2"].Value = "Engineering";
        worksheet["C2"].Value = 95000;
        worksheet["A3"].Value = "James Park";
        worksheet["B3"].Value = "Marketing";
        worksheet["C3"].Value = 78000;
        // Export workbook to a MemoryStream for download
        var stream = workbook.ToStream();
        string filename = "Employees.xlsx";
        var content = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
        // Return file to the browser with content disposition attachment
        return File(stream, content, filename);
    }
}
using IronXL;
using Microsoft.AspNetCore.Mvc;
public class ReportController : Controller
{
    // Export employee data as a downloadable Excel file
    public IActionResult DownloadExcel()
    {
        // Create a new workbook and worksheet
        var workbook = WorkBook.Create(ExcelFileFormat.XLSX);
        var worksheet = workbook.CreateWorkSheet("Employees");
        // Add header row with column names
        worksheet["A1"].Value = "Name";
        worksheet["B1"].Value = "Department";
        worksheet["C1"].Value = "Salary";
        // Populate cells with data values
        worksheet["A2"].Value = "Alice Torres";
        worksheet["B2"].Value = "Engineering";
        worksheet["C2"].Value = 95000;
        worksheet["A3"].Value = "James Park";
        worksheet["B3"].Value = "Marketing";
        worksheet["C3"].Value = 78000;
        // Export workbook to a MemoryStream for download
        var stream = workbook.ToStream();
        string filename = "Employees.xlsx";
        var content = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
        // Return file to the browser with content disposition attachment
        return File(stream, content, filename);
    }
}
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Output Excel File

Download Excel File in ASP .NET C#: Export Data to XLSX, CSV & More: Image 1 - example output for download Excel file in ASP .NET C#

The WorkBook.Create method generates a new Excel document, and CreateWorkSheet adds the first worksheet to it. After populating cells with values, the ToStream method converts the entire workbook into a MemoryStream, no temporary files touch the disk. The File() return method on the controller sets the content disposition header to attachment, which tells the browser to download the file rather than try to render it. The third parameter controls what the file name appears as in the user's download dialog.

This public IActionResult pattern works across .NET Framework and ASP.NET Core projects alike, making it the go-to approach for web applications that need to export data to Excel.

How to Export Database Data to a Downloadable Spreadsheet?

Most real-world scenarios involve exporting data from a database table rather than hardcoded values. The pattern stays the same, query the data, populate worksheets, and return the file. Here's an example that simulates pulling records from a database and writing them into an Excel document.

using IronXL;
using Microsoft.AspNetCore.Mvc;
public class DataExportController : Controller
{
    // Export database records to an xlsx file for download
    public IActionResult ExportDatabaseReport()
    {
        // Simulate a database query returning order records
        var orders = new[]
        {
            new { OrderId = 1001, Customer = "Acme Corp", Total = 4500.00m },
            new { OrderId = 1002, Customer = "Globex Inc", Total = 12300.50m },
            new { OrderId = 1003, Customer = "Initech LLC", Total = 890.75m },
        };
        var workbook = WorkBook.Create(ExcelFileFormat.XLSX);
        var worksheet = workbook.CreateWorkSheet("Orders");
        // Write headers
        worksheet["A1"].Value = "Order ID";
        worksheet["B1"].Value = "Customer";
        worksheet["C1"].Value = "Total";
        // Write each row of data from the query results
        for (int i = 0; i < orders.Length; i++)
        {
            int row = i + 2;
            worksheet[$"A{row}"].Value = orders[i].OrderId;
            worksheet[$"B{row}"].Value = orders[i].Customer;
            worksheet[$"C{row}"].Value = orders[i].Total;
        }
        var stream = workbook.ToStream();
        string filename = $"OrderReport-{DateTime.Now:yyyyMMdd}.xlsx";
        return File(stream, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", filename);
    }
}
using IronXL;
using Microsoft.AspNetCore.Mvc;
public class DataExportController : Controller
{
    // Export database records to an xlsx file for download
    public IActionResult ExportDatabaseReport()
    {
        // Simulate a database query returning order records
        var orders = new[]
        {
            new { OrderId = 1001, Customer = "Acme Corp", Total = 4500.00m },
            new { OrderId = 1002, Customer = "Globex Inc", Total = 12300.50m },
            new { OrderId = 1003, Customer = "Initech LLC", Total = 890.75m },
        };
        var workbook = WorkBook.Create(ExcelFileFormat.XLSX);
        var worksheet = workbook.CreateWorkSheet("Orders");
        // Write headers
        worksheet["A1"].Value = "Order ID";
        worksheet["B1"].Value = "Customer";
        worksheet["C1"].Value = "Total";
        // Write each row of data from the query results
        for (int i = 0; i < orders.Length; i++)
        {
            int row = i + 2;
            worksheet[$"A{row}"].Value = orders[i].OrderId;
            worksheet[$"B{row}"].Value = orders[i].Customer;
            worksheet[$"C{row}"].Value = orders[i].Total;
        }
        var stream = workbook.ToStream();
        string filename = $"OrderReport-{DateTime.Now:yyyyMMdd}.xlsx";
        return File(stream, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", filename);
    }
}
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Output

Download Excel File in ASP .NET C#: Export Data to XLSX, CSV & More: Image 2 - Output for exporting data from a database to an Excel file

In production, the orders array would come from an Entity Framework Core query, a Dapper call, or any data access layer connected via a connection string to the database. The loop iterates through results and writes each value into the correct cells on the worksheet. Note how the string filename includes a date stamp, a small detail that saves headaches when users download files repeatedly.

IronXL's cell addressing system (worksheet[$"A{row}"]) keeps things readable, and the WorkBook API handles all the heavy lifting of building a valid XLSX file internally. For more complex scenarios involving formulas, styling, or multi-sheet workbooks, the same approach scales cleanly.

How to Download Data as CSV Files Instead of XLSX?

Sometimes a lightweight CSV file is the better choice, particularly when feeding data into other systems, databases, or tools that don't need the rich set of features in a real Excel file. IronXL makes switching between formats trivial.

using IronXL;
using Microsoft.AspNetCore.Mvc;
public class CsvController : Controller
{
    // Export data as a CSV file download
    public IActionResult ExportCsv()
    {
        var workbook = WorkBook.Create(ExcelFileFormat.XLSX);
        var worksheet = workbook.CreateWorkSheet("Products");
        worksheet["A1"].Value = "SKU";
        worksheet["B1"].Value = "Product";
        worksheet["C1"].Value = "Price";
        worksheet["A2"].Value = "WDG-001";
        worksheet["B2"].Value = "Widget Pro";
        worksheet["C2"].Value = 29.99;
        // Convert to CSV stream instead of XLSX
        var stream = workbook.ToCsvStream();
        string filename = "Products.csv";
        return File(stream, "text/csv", filename);
    }
}
using IronXL;
using Microsoft.AspNetCore.Mvc;
public class CsvController : Controller
{
    // Export data as a CSV file download
    public IActionResult ExportCsv()
    {
        var workbook = WorkBook.Create(ExcelFileFormat.XLSX);
        var worksheet = workbook.CreateWorkSheet("Products");
        worksheet["A1"].Value = "SKU";
        worksheet["B1"].Value = "Product";
        worksheet["C1"].Value = "Price";
        worksheet["A2"].Value = "WDG-001";
        worksheet["B2"].Value = "Widget Pro";
        worksheet["C2"].Value = 29.99;
        // Convert to CSV stream instead of XLSX
        var stream = workbook.ToCsvStream();
        string filename = "Products.csv";
        return File(stream, "text/csv", filename);
    }
}
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Output CSV File

Download Excel File in ASP .NET C#: Export Data to XLSX, CSV & More: Image 3 - Data downloaded as a CSV file instead of Excel

The ToCsvStream method exports the first worksheet as a CSV-formatted MemoryStream. CSV files work great for data interchange, but they strip out any formatting, formulas, and multi-sheet structure. When you need those features, stick with the XLSX file format via ToStream() or ToXlsxStream(). For a deeper look at format conversions, refer to the spreadsheet conversion guide.

How to Re-Export an Upload in a Different Format?

A common web application scenario involves accepting uploaded files from users and exporting them in another format, say, converting an XLS upload to XLSX, or producing CSV files from a workbook originally saved in a legacy format.

public IActionResult ConvertUpload(IFormFile upload)
{
    using var memoryStream = new MemoryStream();
    upload.CopyTo(memoryStream);
    memoryStream.Position = 0;
    // Load uploaded Excel file from the stream
    var workbook = WorkBook.Load(memoryStream);
    // Re-export as XLSX regardless of the original file extension or file type
    var stream = workbook.ToXlsxStream();
    string filename = Path.GetFileNameWithoutExtension(upload.FileName) + ".xlsx";
    return File(stream, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", filename);
}
public IActionResult ConvertUpload(IFormFile upload)
{
    using var memoryStream = new MemoryStream();
    upload.CopyTo(memoryStream);
    memoryStream.Position = 0;
    // Load uploaded Excel file from the stream
    var workbook = WorkBook.Load(memoryStream);
    // Re-export as XLSX regardless of the original file extension or file type
    var stream = workbook.ToXlsxStream();
    string filename = Path.GetFileNameWithoutExtension(upload.FileName) + ".xlsx";
    return File(stream, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", filename);
}
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Output: Converting CSV to XLSX Format

Download Excel File in ASP .NET C#: Export Data to XLSX, CSV & More: Image 4 - Example output for converting our CSV file to XLSX format

The WorkBook.Load method accepts a MemoryStream, so there's no need to save uploaded files to disk first. It auto-detects whether the source is an XLS, XLSX, or CSV file and parses it accordingly. From there, ToXlsxStream() generates a clean new MemoryStream in the modern XLSX format, every byte properly structured. This is useful for normalizing user submissions before further processing or storage.

Which File Formats Can Be Exported?

IronXL supports exporting data to multiple spreadsheet and data interchange formats. The table below summarizes the available output options and their best uses.

| Format | File Extension | Stream Method | Best Use Case | | --- | --- | --- | --- | | XLSX | .xlsx | ToXlsxStream() | Modern Excel spreadsheets with formatting and formulas | | XLS | .xls | ToXlsStream() | Legacy system compatibility | | CSV | .csv | ToCsvStream() | Database imports, data pipelines, lightweight export | | XML | .xml | ToXmlStream() | Enterprise system integration | | JSON | .json | SaveAsJson() | Web API responses and data exchange | | HTML | .html | ExportToHtml() | Web page display of spreadsheet data |

Every stream method returns a MemoryStream that plugs directly into ASP.NET Core's File() return helper. The byte array alternative (ToByteArray()) is also available for scenarios where a byte[] is more convenient, for example, when saving to a blob database or attaching to an email response stream. All of these methods are available immediately after installing the IronXL NuGet package. For a complete walkthrough of each export format, see the export to Excel documentation.

Whether the goal is to download files in XLSX format for business analysts, export CSV files for data engineers, or generate XML for enterprise integration, IronXL keeps the code clean and the output reliable across .NET Core and .NET Framework applications. Ready to ship spreadsheet exports in your next project? Get a free trial license or explore licensing options to get started today. For step-by-step setup instructions, refer to the IronXL getting started guide.

Jordi Bardia
Jordi Bardia
  Chat with engineering team now
Software Engineer
Jordi is most proficient in Python, C# and C++, when he isn’t leveraging his skills at Iron Software; he’s game programming. Sharing responsibilities for product testing, product development and research, Jordi adds immense value to continual product improvement. The varied experience keeps him challenged and engaged, and he ...
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