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Document format

XLSB converter

An .xlsb file is a Microsoft Excel workbook whose sheets are stored as binary BIFF12 records instead of XML. The packaging is the same ZIP as .xlsx, but each worksheet is a .bin part, which makes very large workbooks noticeably faster to open and smaller on disk.

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Drop XLSB files here

Batch files can each use a different output. Nothing uploads for local conversions.

Working inputs include camera RAW, browser-local audio/video, PDF, CBZ/CBR comics, office documents, ebooks, markup, 3D models, structured text, images, and archives.

Where XLSB comes from

Excel 2007 shipped .xlsb alongside .xlsx as a performance-oriented alternative, reusing the OOXML package while keeping a binary cell encoding descended from the old BIFF record streams. Microsoft documented the record format as MS-XLSB, so it is an open specification rather than a closed one.

How XLSB works

  • OOXML ZIP package whose worksheets are xl/worksheets/sheetN.bin rather than XML.
  • Cells are typed BIFF12 records, so parsing skips XML tokenizing entirely — the reason it loads faster.
  • Same grid limits as .xlsx: 1,048,576 rows by 16,384 columns per sheet.
  • A .xlsb workbook may carry a VBA macro project; Novus Convert reads it with macro retention switched off and formula text switched off, so only the values already computed by Excel are taken and nothing is interpreted or executed.
  • Decoded here by SheetJS, the same reader that already backs the legacy .xls route.

When to use XLSB

  • Very large models where .xlsx open and save times have become painful.
  • Workbooks pushed around a network where file size matters.
  • Long-running financial models with heavy formula counts.
  • Extracting data from a binary workbook into CSV, JSON, or plain .xlsx.

Strengths and limitations

Strengths

  • Substantially faster to open and save than an equivalent .xlsx.
  • Noticeably smaller on disk for the same content.
  • Publicly documented as MS-XLSB, so third-party readers are possible.

Limitations

  • Far less widely supported than .xlsx outside Microsoft's own tools.
  • Binary content is opaque to diff, grep, and version control.
  • Can carry macros without saying so in the extension, unlike the .xlsx/.xlsm split.

Compatibility

Excel 2007 onward on Windows and macOS reads and writes .xlsb. LibreOffice Calc imports it, Google Sheets and Excel for the web do not accept it directly, and most data libraries need an explicit binary reader. In-browser conversion here handles it through SheetJS.

docProps/core.xml and docProps/app.xml remain XML inside the package, so author and application metadata survive there even though the cells are binary.

Convert XLSB to another format