.NET Core Excel Spreadsheet: Create Professional Excel Worksheet Files in C# Using IronXL

How Do I Create Excel Spreadsheets in .NET Core Without Office Dependencies?

Traditional Microsoft Excel automation requires MS Office installation and uses Office Interop, which doesn't work on Linux or in containerized environments. As discussed in Microsoft's documentation, Office Interop also introduces deployment complexity and licensing concerns. IronXL for .NET eliminates these limitations by providing a pure .NET solution that processes Excel files natively with full support for modern spreadsheet capabilities.

The library supports .NET 8, .NET 9, and .NET 10, along with earlier .NET Core versions. It handles XLSX, XLS, CSV, and other spreadsheet formats without external dependencies. This makes it particularly valuable for server-side applications, microservices, and scenarios where installing Microsoft Office isn't practical. Easy integration via NuGet package installation means developers can start writing Excel files within minutes. Open Visual Studio, then access the NuGet Package Manager Console and run the following command:

Install-Package IronXL.Excel

using IronXL;
// Create a new workbook in XLSX format
WorkBook workbook = WorkBook.Create(ExcelFileFormat.XLSX);
// Add an Excel worksheet with a custom name
WorkSheet sheet = workbook.CreateWorkSheet("SalesReport");
// Set a cell value
sheet["A1"].Value = "Product Sales Summary";
// Save the generated Excel file
workbook.SaveAs("SalesReport.xlsx");

using IronXL;
// Create a new workbook in XLSX format
WorkBook workbook = WorkBook.Create(ExcelFileFormat.XLSX);
// Add an Excel worksheet with a custom name
WorkSheet sheet = workbook.CreateWorkSheet("SalesReport");
// Set a cell value
sheet["A1"].Value = "Product Sales Summary";
// Save the generated Excel file
workbook.SaveAs("SalesReport.xlsx");

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The WorkBook.Create() method initializes a new Excel workbook, accepting an ExcelFileFormat parameter to specify XLSX (modern XML-based format introduced in Excel 2007) or XLS (legacy binary format). XLSX is recommended for most scenarios due to smaller file sizes and better compatibility with modern tools. The CreateWorkSheet() method adds named worksheets where Excel data lives—each workbook can contain multiple individual sheets for organizing related data.

What Are the Steps to Add Worksheets and Populate Data?

Real-world Excel spreadsheets contain structured data across multiple worksheets. IronXL provides flexible methods for organizing information and populating cells efficiently, whether working with manual data entry or automated data pipelines in data-driven applications.

using IronXL;
WorkBook workbook = WorkBook.Create(ExcelFileFormat.XLSX);
WorkSheet sheet = workbook.CreateWorkSheet("MonthlySales");
// Set column names as headers
sheet["A1"].Value = "Month";
sheet["B1"].Value = "Revenue";
sheet["C1"].Value = "Units Sold";
// Populate Excel data using a loop (mock sales data)
string[] months = { "January", "February", "March", "April", "May", "June" };
decimal[] revenue = { 45000.50m, 52000.75m, 48500.25m, 61000.00m, 58750.50m, 67200.25m };
int[] units = { 150, 175, 160, 200, 190, 220 };
for (int i = 0; i < months.Length; i++)
{
    int row = i + 2;
    sheet[$"A{row}"].Value = months[i];
    sheet[$"B{row}"].Value = revenue[i];
    sheet[$"C{row}"].Value = units[i];
}
// Set a range of cells to the same value across columns
sheet["D2:D7"].Value = "Active";
workbook.SaveAs("MonthlySales.xlsx");

using IronXL;
WorkBook workbook = WorkBook.Create(ExcelFileFormat.XLSX);
WorkSheet sheet = workbook.CreateWorkSheet("MonthlySales");
// Set column names as headers
sheet["A1"].Value = "Month";
sheet["B1"].Value = "Revenue";
sheet["C1"].Value = "Units Sold";
// Populate Excel data using a loop (mock sales data)
string[] months = { "January", "February", "March", "April", "May", "June" };
decimal[] revenue = { 45000.50m, 52000.75m, 48500.25m, 61000.00m, 58750.50m, 67200.25m };
int[] units = { 150, 175, 160, 200, 190, 220 };
for (int i = 0; i < months.Length; i++)
{
    int row = i + 2;
    sheet[$"A{row}"].Value = months[i];
    sheet[$"B{row}"].Value = revenue[i];
    sheet[$"C{row}"].Value = units[i];
}
// Set a range of cells to the same value across columns
sheet["D2:D7"].Value = "Active";
workbook.SaveAs("MonthlySales.xlsx");

IRON VB CONVERTER ERROR developers@ironsoftware.com

String interpolation ($"A{row}") enables dynamic cell addressing within loops, making it straightforward to populate rows programmatically from any data source. The range syntax sheet["D2:D7"] applies values to multiple cells simultaneously—useful for status columns, default values, or initializing data regions. IronXL automatically handles data type conversion, storing decimals as numeric values and string content as text while preserving appropriate Excel data types for the generated Excel file.

For applications requiring database integration, IronXL works seamlessly with Entity Framework Core, Dapper, or raw ADO.NET. Data from DataTable objects can be exported directly to worksheets, simplifying reporting workflows and allowing users to share data across systems.

Creating multiple worksheets organizes related Excel data logically within a single workbook:

WorkSheet summarySheet = workbook.CreateWorkSheet("Summary");
WorkSheet detailSheet = workbook.CreateWorkSheet("Details");
WorkSheet archiveSheet = workbook.CreateWorkSheet("Archive");

WorkSheet summarySheet = workbook.CreateWorkSheet("Summary");
WorkSheet detailSheet = workbook.CreateWorkSheet("Details");
WorkSheet archiveSheet = workbook.CreateWorkSheet("Archive");

IRON VB CONVERTER ERROR developers@ironsoftware.com

Learn more about managing worksheets and writing Excel files in the IronXL documentation. For reading an existing Excel file, see the Excel file loading tutorial.

How Do I Apply Professional Formatting and Styling?

Raw data becomes meaningful when properly formatted. IronXL supports background colors, fonts, borders, and number formats—essential formatting capabilities that transform Excel spreadsheets into polished reports suitable for executive presentations or client deliverables.

using IronXL;
WorkBook workbook = WorkBook.Create(ExcelFileFormat.XLSX);
WorkSheet sheet = workbook.CreateWorkSheet("FormattedReport");
// Create headers with styling
sheet["A1"].Value = "Category";
sheet["B1"].Value = "Amount";
sheet["C1"].Value = "Date";
// Apply header formatting to the Excel sheet
sheet["A1:C1"].Style.SetBackgroundColor("#2E86AB");
sheet["A1:C1"].Style.Font.Bold = true;
sheet["A1:C1"].Style.Font.SetColor("#FFFFFF");
// Add sample data to specific cells
sheet["A2"].Value = "Software License";
sheet["B2"].Value = 1299.99m;
sheet["C2"].Value = DateTime.Now;
// Format currency and date columns
sheet["B2"].FormatString = "$#,##0.00";
sheet["C2"].FormatString = "yyyy-MM-dd";
// Add borders around the data range
var dataRange = sheet["A1:C2"];
dataRange.Style.BottomBorder.SetColor("#000000");
dataRange.Style.BottomBorder.Type = IronXL.Styles.BorderType.Thin;
workbook.SaveAs("FormattedReport.xlsx");

using IronXL;
WorkBook workbook = WorkBook.Create(ExcelFileFormat.XLSX);
WorkSheet sheet = workbook.CreateWorkSheet("FormattedReport");
// Create headers with styling
sheet["A1"].Value = "Category";
sheet["B1"].Value = "Amount";
sheet["C1"].Value = "Date";
// Apply header formatting to the Excel sheet
sheet["A1:C1"].Style.SetBackgroundColor("#2E86AB");
sheet["A1:C1"].Style.Font.Bold = true;
sheet["A1:C1"].Style.Font.SetColor("#FFFFFF");
// Add sample data to specific cells
sheet["A2"].Value = "Software License";
sheet["B2"].Value = 1299.99m;
sheet["C2"].Value = DateTime.Now;
// Format currency and date columns
sheet["B2"].FormatString = "$#,##0.00";
sheet["C2"].FormatString = "yyyy-MM-dd";
// Add borders around the data range
var dataRange = sheet["A1:C2"];
dataRange.Style.BottomBorder.SetColor("#000000");
dataRange.Style.BottomBorder.Type = IronXL.Styles.BorderType.Thin;
workbook.SaveAs("FormattedReport.xlsx");

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The Style property exposes formatting options matching Microsoft Excel's capabilities. Background colors accept hex codes (with or without the # prefix), while FormatString applies number formats identical to Excel's custom formatting syntax—the same patterns work in both environments. Border styling supports various types including Thin, Medium, Thick, and Double, allowing precise control over cell boundaries in your Excel worksheet.

For Excel spreadsheets with extensive data, CreateFreezePane(0, 1) keeps headers visible while scrolling—a subtle enhancement that significantly improves usability for large datasets with better spreadsheet performance. Print configuration through sheet.PrintSetup handles orientation, margins, and scaling for physical output.

Explore additional styling options in the cell formatting guide and border configuration tutorial. These tools give developers complete access to edit and customize every aspect of cell appearance.

How Can I Use Excel Formulas for Calculations?

Excel's calculation engine is a core function that automates data analysis, and IronXL provides full support for formulas. Set formulas as strings using standard Excel syntax, and IronXL calculates results automatically when requested—essential for reporting and financial analysis.

using IronXL;
WorkBook workbook = WorkBook.Create(ExcelFileFormat.XLSX);
WorkSheet sheet = workbook.CreateWorkSheet("BudgetCalculations");
// Add expense data to the Excel workbook
sheet["A1"].Value = "Expense";
sheet["B1"].Value = "Amount";
sheet["A2"].Value = "Rent";
sheet["B2"].Value = 2500;
sheet["A3"].Value = "Utilities";
sheet["B3"].Value = 350;
sheet["A4"].Value = "Supplies";
sheet["B4"].Value = 875;
sheet["A5"].Value = "Marketing";
sheet["B5"].Value = 1200;
// Add formulas for calculations
sheet["A7"].Value = "Total:";
sheet["B7"].Formula = "=SUM(B2:B5)";
sheet["A8"].Value = "Average:";
sheet["B8"].Formula = "=AVERAGE(B2:B5)";
sheet["A9"].Value = "Maximum:";
sheet["B9"].Formula = "=MAX(B2:B5)";
sheet["A10"].Value = "Count:";
sheet["B10"].Formula = "=COUNT(B2:B5)";
// Calculate all formulas
workbook.EvaluateAll();
// Access calculated values programmatically
decimal total = sheet["B7"].DecimalValue;
Console.WriteLine($"Calculated total: {total}");
workbook.SaveAs("BudgetCalculations.xlsx");

using IronXL;
WorkBook workbook = WorkBook.Create(ExcelFileFormat.XLSX);
WorkSheet sheet = workbook.CreateWorkSheet("BudgetCalculations");
// Add expense data to the Excel workbook
sheet["A1"].Value = "Expense";
sheet["B1"].Value = "Amount";
sheet["A2"].Value = "Rent";
sheet["B2"].Value = 2500;
sheet["A3"].Value = "Utilities";
sheet["B3"].Value = 350;
sheet["A4"].Value = "Supplies";
sheet["B4"].Value = 875;
sheet["A5"].Value = "Marketing";
sheet["B5"].Value = 1200;
// Add formulas for calculations
sheet["A7"].Value = "Total:";
sheet["B7"].Formula = "=SUM(B2:B5)";
sheet["A8"].Value = "Average:";
sheet["B8"].Formula = "=AVERAGE(B2:B5)";
sheet["A9"].Value = "Maximum:";
sheet["B9"].Formula = "=MAX(B2:B5)";
sheet["A10"].Value = "Count:";
sheet["B10"].Formula = "=COUNT(B2:B5)";
// Calculate all formulas
workbook.EvaluateAll();
// Access calculated values programmatically
decimal total = sheet["B7"].DecimalValue;
Console.WriteLine($"Calculated total: {total}");
workbook.SaveAs("BudgetCalculations.xlsx");

IRON VB CONVERTER ERROR developers@ironsoftware.com

The Formula property accepts standard Excel formula syntax—the same formulas that work in Microsoft Excel work here. After setting formulas, call EvaluateAll() to compute results. This step ensures calculated values are available immediately through typed properties like DecimalValue, IntValue, or StringValue. Without calling EvaluateAll(), formulas still save correctly and calculate when opened in Excel, but programmatic access to results requires evaluation first.

decimal sum = sheet["B2:B5"].Sum();
decimal avg = sheet["B2:B5"].Avg();
decimal max = sheet["B2:B5"].Max();

decimal sum = sheet["B2:B5"].Sum();
decimal avg = sheet["B2:B5"].Avg();
decimal max = sheet["B2:B5"].Max();

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How Do I Export Excel Files and Serve Them for Download?

IronXL supports multiple export formats to meet different integration requirements. Beyond standard Excel formats, spreadsheets can export to CSV for data interchange, JSON for web applications, or TSV for legacy system compatibility. This flexibility makes it easy to integrate Excel generation into any workflow.

using IronXL;
WorkBook workbook = WorkBook.Load("BudgetCalculations.xlsx");
// Export to different formats - save the Excel data as needed
workbook.SaveAs("output.xlsx");      // Modern Excel (Office 2007+)
workbook.SaveAs("output.xls");       // Legacy Excel (97-2003)
workbook.SaveAsCsv("output.csv");    // CSV for data import/export
workbook.SaveAsJson("output.json");  // JSON for web APIs

using IronXL;
WorkBook workbook = WorkBook.Load("BudgetCalculations.xlsx");
// Export to different formats - save the Excel data as needed
workbook.SaveAs("output.xlsx");      // Modern Excel (Office 2007+)
workbook.SaveAs("output.xls");       // Legacy Excel (97-2003)
workbook.SaveAsCsv("output.csv");    // CSV for data import/export
workbook.SaveAsJson("output.json");  // JSON for web APIs

IRON VB CONVERTER ERROR developers@ironsoftware.com

Each format serves specific use cases. XLSX works best for preserving formatting and formulas when sharing with Excel users. CSV provides maximum compatibility for importing into databases, analytics tools, or other spreadsheet applications. JSON integrates naturally with JavaScript frontends and REST APIs. For document workflows, consider integrating with PDF generation tools to convert your Excel data to PDF.

[HttpGet("download-report")]
public IActionResult DownloadReport()
{
    WorkBook workbook = WorkBook.Create(ExcelFileFormat.XLSX);
    WorkSheet sheet = workbook.CreateWorkSheet("Report");
    sheet["A1"].Value = "Generated Report";
    sheet["A2"].Value = DateTime.Now;
    var stream = workbook.ToStream();
    return File(stream,
        "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
        "Report.xlsx");
}

[HttpGet("download-report")]
public IActionResult DownloadReport()
{
    WorkBook workbook = WorkBook.Create(ExcelFileFormat.XLSX);
    WorkSheet sheet = workbook.CreateWorkSheet("Report");
    sheet["A1"].Value = "Generated Report";
    sheet["A2"].Value = DateTime.Now;
    var stream = workbook.ToStream();
    return File(stream,
        "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
        "Report.xlsx");
}

IRON VB CONVERTER ERROR developers@ironsoftware.com

Performance and Security Considerations for Excel Generation

When building applications that generate Excel files in .NET Core, both performance and security are top priorities—especially as users expect fast, reliable, and secure spreadsheet solutions. The modern .NET Core spreadsheet control is engineered to deliver high-performance Excel file generation, making it possible to create and manipulate even the most complex Excel worksheets without the overhead of Microsoft Office or Office Interop.

For optimal spreadsheet performance, the .NET Core spreadsheet control leverages advanced techniques like data virtualization. This means your application can efficiently process and export large volumes of data to Excel files, without running into memory bottlenecks or slowdowns. Multi-threading support further enhances performance by allowing concurrent processing of multiple Excel file generation tasks, ensuring that even data-heavy operations complete quickly and efficiently.

Security is equally important when working with Excel files, especially when handling sensitive or confidential data. By operating independently of Microsoft Office and avoiding Office Interop, the .NET Core spreadsheet control minimizes the risk of external vulnerabilities and ensures a more secure environment for your .NET applications. Additionally, built-in support for encryption and password protection allows you to safeguard your generated Excel files, ensuring that only authorized users can access or edit critical worksheets and data.

Why Choose This Library Over Other .NET Excel Solutions?

Several libraries exist for .NET Excel manipulation, each with different strengths. Here's how IronXL compares as a solution for creating and managing Excel files:

Conclusion

Creating .NET Core Excel spreadsheets with IronXL streamlines what was once a complex, dependency-heavy task. From basic cell manipulation to formula calculations and professional formatting, the library provides a complete toolkit for spreadsheet automation that runs anywhere .NET runs—Windows servers, Linux containers, or cloud platforms.

The cross-platform architecture ensures identical behavior across development machines and production environments, eliminating the "works on my machine" problems common with Office Interop solutions. As noted in .NET Foundation discussions, modern .NET development increasingly targets cross-platform deployment, making Office-independent libraries essential for maintainable solutions and better system compatibility.

Ready to start building? Download a free 30-day trial to explore all features with no limitations, or view licensing options for production deployment. For additional code examples covering advanced scenarios like reading an existing Excel file or working with password-protected workbooks, browse the complete documentation and API reference.