AutoFitColumns with AutoFilter allocates insufficient width for dropdown arrow (header text collides with button)

[lievendf]

Environment / EPPlus version / Spreadsheet application

Windows / 8.7.0 / Excel

Description

When applying AutoFitColumns() on a range with AutoFilter enabled, the calculated column widths are too narrow for columns whose width is determined by the header text. When opened in Excel, the header text sits directly against the left edge of the filter dropdown button with 0px margin/padding.

Cause

In OfficeOpenXml.Core.AutofitHelper:

private const double AutoFilterArrowWidthPixels = 15d;

1. On Windows 10/11 (96 DPI / 100% scaling), the native Excel filter dropdown arrow button is exactly 17 pixels wide.
2. Native Excel AutoFit also includes inner cell padding / text margin between the text end and the button.
3. Because EPPlus only adds 15px / fontWidth, the resulting column is narrower than native Excel AutoFit.

Steps to Reproduce

using System.IO;
using OfficeOpenXml;
using OfficeOpenXml.SystemDrawing.Text;

ExcelPackage.License.SetNonCommercialPersonal("NonCommercial");

using (var package = new ExcelPackage(new FileInfo("autofilter_autofit_test.xlsx")))
{
    package.Settings.TextSettings.PrimaryTextMeasurer = new SystemDrawingTextMeasurer();
    package.Workbook.DefaultThemeVersion = 166925; // Calibri

    var ws = package.Workbook.Worksheets.Add("AutoFilterTest");

    ws.Cells["A1"].Value = "Text";
    ws.Cells["B1"].Value = "Number";
    ws.Cells["C1"].Value = "decField";
    ws.Cells["D1"].Value = "dateField";
    ws.Cells["E1"].Value = "logField";
    ws.Cells["A1:E1"].Style.Font.Bold = true;

    ws.Cells["A2"].Value = "Row 1 Alpha";
    ws.Cells["B2"].Value = 42;
    ws.Cells["C2"].Value = 123.45;
    ws.Cells["D2"].Value = "01/15/2026";
    ws.Cells["E2"].Value = "yes";

    ws.Cells["A3"].Value = "Row 2 Beta";
    ws.Cells["B3"].Value = 99;
    ws.Cells["C3"].Value = 678.90;
    ws.Cells["D3"].Value = "02/20/2026";
    ws.Cells["E3"].Value = "no";

    ws.Cells["A1:E3"].AutoFilter = true;
    ws.Cells["A1:E3"].AutoFitColumns(2.0);

    package.Save();
}

Expected Behavior

Column width should reserve space for both the 17px arrow button and some padding, more closely matching native Excel AutoFit.

Suggested Fix

In AutofitHelper.cs, increase AutoFilterArrowWidthPixels from 15d to at least 17d or even a bit more.

[swmal]

Hello @lievendf,

we can do this it is a simple fix.

/Mats

[swmal]

I have increased the value from 15 to 19. Will be included in next release.