Office Open XML Spreadsheet (XLSX) stores cell values, formulas, formatting, and charts as zipped XML, the default format for Microsoft Excel 2007 and later. Windows Icon (ICO) bundles multiple raster images at different resolutions (16x16 through 256x256) into a single file for use as application icons. This conversion changes the file's encoding, compression method, and supported feature set. Metadata such as creation date and embedded colour profiles is preserved where the target format supports it. The result is a standard ICO file readable by any compatible application. 1converter handles XLSX-to-ICO conversion server-side: files are uploaded over HTTPS, processed on isolated cloud infrastructure, and the converted output is available for download for 24 hours before automatic deletion. No account is required for standard conversions.