History Lesson: What Is a .ods File? Why Excel Opens It but Formulas Change

What is a .ods file?

A .ods file is the spreadsheet member of the OpenDocument Format (ODF), the open standard for office files whose siblings include .odt text documents, .odp presentations, and .odg drawings. It is the native workbook format of LibreOffice Calc and Apache OpenOffice Calc, and programs such as Microsoft Excel, Google Sheets, and Gnumeric can open or save it. Its official media type is application/vnd.oasis.opendocument.spreadsheet. A spreadsheet template uses .ots, and a .fods is the “flat” variant: the same XML in one uncompressed file instead of a ZIP.

Why does Excel open it, but formulas or formatting change?

Because Excel does not keep the file as OpenDocument while you work. It reads the package, maps every sheet, style, and formula into its own model, and writes OpenDocument back out only when you save. Microsoft’s support page comparing .ods with .xlsx lists what survives the trip. Basic cell formatting, cell styles, print ranges, and formulas are supported. But dates before 1 January 1900 do not save correctly, repeat rows and columns for printing are not supported, table styles and total rows are lost, threaded comments turn into old-style comments, and a workbook with a password-protected sheet cannot be saved or opened. Microsoft’s list of Excel file formats puts it plainly: formatting might be lost when saving and opening .ods files.

Formulas are a separate story. Inside a .ods, a formula cell carries a table:formula attribute whose text starts with a namespace prefix, a short tag that says which formula language the rest of the string is written in. Microsoft’s implementation notes for Excel 2013 and later say Excel loads the formula if the prefix is of (OpenFormula), msoxl (Excel’s own syntax), or missing. With any other prefix, Excel skips the formula and keeps only the last calculated value stored in the cell. The cell looks right, but it has become a fixed number that will not recalculate.

1985–2002: StarCalc, Sun, and OpenOffice.org Calc

The family starts with Star Division, founded in 1985 in Lüneburg, Germany, by Marco Börries. Its StarOffice suite grew a spreadsheet, StarCalc; StarOffice 2.0 in 1994 bundled StarWriter, StarCalc, and StarBase for Windows 3.1. Those StarCalc workbooks were binary .sdc files, a different animal altogether — see History Lesson: What Is a .sdc File?.

Sun Microsystems bought Star Division in August 1999, and on 19 July 2000 announced that it would release the StarOffice source code as OpenOffice.org, a project that would also coordinate, in Sun’s words, “the definition of XML-based file formats.” OpenOffice.org 1.0 arrived on 1 May 2002, and its Calc saved .sxc files: a ZIP package of XML parts instead of a binary blob. That package design is the direct ancestor of .ods — see History Lesson: What Is a .sxc File?.

2005: OASIS, ODF 1.0, and ISO/IEC 26300

To turn that package into a vendor-neutral standard, it went to OASIS, the Organization for the Advancement of Structured Information Standards, a non-profit consortium that publishes open technical standards. Its OpenDocument technical committee first met on 16 December 2002, and ODF 1.0 was approved as an OASIS Standard on 1 May 2005. OpenOffice.org 2.0, released on 20 October 2005, made OpenDocument its default format, and .ods files started replacing .sxc on ordinary PCs.

OASIS then submitted ODF to the joint committee of ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission). It passed its ballot on 3 May 2006 and was published as ISO/IEC 26300:2006 on 30 November 2006. Later versions followed: ODF 1.1 in February 2007, ODF 1.2 in September 2011 (published by ISO/IEC in 2015), ODF 1.3 in April 2021, and ODF 1.4, approved on 6 October 2025.

How the bytes work: a ZIP of XML, one cell at a time

Open a .ods in a hex viewer and the first two bytes spell PK, the signature of a ZIP archive. The ODF packaging rules require a small file named mimetype to come first, stored uncompressed, containing only the text application/vnd.oasis.opendocument.spreadsheet, so software can recognize the workbook without unpacking it. After it come content.xml (the sheets and cells), styles.xml (formatting), meta.xml (author and dates), settings.xml (view settings), and META-INF/manifest.xml, the list of every part. XML, short for Extensible Markup Language, is plain text built from tags, so once unzipped the whole workbook can be read in a text editor.

Inside content.xml, each sheet is a table:table element, each row a table:table-row, and each cell a table:table-cell. A cell does not just hold text: it declares its kind of value with an office:value-type attribute — float, percentage, currency, date, time, boolean, or string — and keeps the raw value in a separate attribute, while a paragraph inside the cell holds the version you see on screen. That split is why a cell can display 12% while storing 0.12. Runs of identical or empty cells are compressed with a repeat count (table:number-columns-repeated) instead of being written out one by one.

The formula gap: from ODF 1.0 to OpenFormula

The first standard described where a formula lives — the table:formula attribute — but not the language inside it. The Library of Congress’s format description notes that ODS 1.1 “allowed any syntax for strings representing formulas,” and that this shortcoming led to interoperability problems. In practice, OpenOffice.org wrote its formulas behind an oooc: prefix, with cell references in square brackets such as [.A1], and several other ODF programs wrote formulas the same way.

When Microsoft Office 2007 Service Pack 2 added built-in ODF support on 28 April 2009, Excel took a different path. Microsoft’s implementation notes said Excel 2007 saved formulas behind its own msoxl prefix in Excel syntax and, when loading, kept only the stored value for formulas in any other namespace. A Microsoft blog argued that because ODF 1.0 and 1.1 did not define formulas, every ODF spreadsheet implementation was application-dependent. Rob Weir of IBM, co-chair of the OASIS ODF committee, published tests in May 2009 showing that SP2 stripped the formulas out of spreadsheets made by other ODF programs, leaving only their last values. The dispute became a textbook case of why a file format needs a formula standard, not just a cell structure.

That standard is OpenFormula, Part 2 of ODF 1.2 (an OASIS Standard since 29 September 2011). It defines data types, syntax, and the behavior of built-in functions so that a formula gives equivalent results in different programs, and ODF 1.2 formulas carry the of: prefix. Excel added ODF 1.2 support in Office 2013 and now saves formulas with that prefix. Read Microsoft’s rules closely, though, and the older oooc: prefix is not on Excel’s list — which is one reason a .ods saved by a 2000s-era suite may open in Excel with values where formulas used to be.

LibreOffice, governments, and a format nobody owns

Oracle bought Sun in 2010. On 28 September 2010 community developers announced The Document Foundation and the LibreOffice fork, and on 1 June 2011 Oracle gave the OpenOffice.org code to the Apache Software Foundation, where it continues as Apache OpenOffice. Both still save new spreadsheets as .ods by default.

Governments helped carry .ods beyond enthusiasts. In September 2005 the Commonwealth of Massachusetts published a policy requiring its executive-branch agencies to save office documents in OpenDocument by 1 January 2007; a 2007 revision also accepted Microsoft’s Open XML. On 22 July 2014 the UK government chose ODF as its standard for sharing and collaborating on government documents. In March 2026 Germany’s IT planning council adopted a set of Deutschland-Stack standards that names ODF for documents.

Why .ods files are still on disks in 2026

Because .ods has been the free default for two decades. Every LibreOffice and OpenOffice install saves a new workbook as .ods unless someone changes the setting, so school computers, charities, small offices, Linux desktops, and anyone who skipped buying Microsoft Office have folders of .ods budgets, class lists, inventories, and club accounts. Many of those workbooks are now legacy files: made in a suite that is no longer installed, written by an older version whose formulas a modern Excel may treat as fixed values, or needed as .xlsx by someone who has never heard of OpenDocument.

When you need .xlsx, CSV, or PDF instead

Renaming .ods to .xlsx does nothing: the parts inside are still OpenDocument XML, and .xlsx is a different standard, Office Open XML, published as ISO/IEC 29500 in November 2008. A real conversion reads the OpenDocument cells and writes a new file. Pick XLSX when someone needs to keep working in Excel, CSV when only the values matter, and PDF when the sheet must print the same everywhere. Then spot-check formulas, dates, and protected sheets, because those are where the two formats disagree.

Legacy File Converter opens .ods and flat .fods workbooks on your own Windows PC and saves them as XLSX, PDF, CSV, Markdown, or HTML — nothing is uploaded, which matters when the sheet holds payroll or member details. For earlier generations of the same spreadsheet, see StarCalc .sdc and OpenOffice.org Calc .sxc; for Excel’s side of the story, see History Lesson: What Is a .xls File?.