XLS to XLSX Converter
Convert XLS to XLSX online for free. Fast, secure, and high-quality conversion with no sign-up or software required.
Maximum file size is 1GB
How it works
Three steps to your converted file
Everything happens in your browser tab - upload, pick a format, download. The heavy lifting runs on our servers.
Upload your file
Drag and drop, click to browse, or paste a URL. Batches take up to 20 files at once - 230+ input formats across video, audio, image, document, and archive types.
Choose an output format
Pick from over a hundred output formats. Filter by category or search by name - every option is open to everyone, no account needed.
Convert & download
Hit Convert and grab your download link moments later. Originals are erased when the job completes; results are cleared within about an hour.
What is an XLS file?
The XLS format utilizes the Binary Interchange File Format (BIFF) scheme, serving as the default spreadsheet standard for Microsoft Excel from versions 2.0 through 2003. Encapsulated within the Object Linking and Embedding (OLE) Compound File Binary Format (CFBF), XLS files store data in binary streams rather than XML. This proprietary structure supports formulas, Visual Basic for Applications (VBA) macros, and charts but lacks the compression efficiency and corruption resilience of the newer XML-based standards.
How to open an XLS file
Microsoft Excel remains the primary software for full fidelity access to XLS files. On Windows and macOS, the operating system associates these files with the Office suite if installed. Alternatively, open-source solutions like LibreOffice Calc and Gnumeric provide robust reverse-engineered support for reading and editing XLS binaries on Linux and other platforms without requiring Microsoft licenses.
XLS Technical Info
- Full Name
- Excel Binary File Format
- Developed By
- Microsoft
- Initial Release
- 1987
- MIME Type
- application/vnd.ms-excel
What is an XLSX file?
The XLSX format is the default XML-based spreadsheet file introduced in Microsoft Office 2007, adhering to the Office Open XML (OOXML) standard (ECMA-376 and ISO/IEC 29500). It replaces the binary BIFF structure of legacy XLS files with a ZIP-compressed container holding individual XML files for workbook data, worksheet structure, and metadata. By design, XLSX files strictly exclude Visual Basic for Applications (VBA) macros to prevent malware propagation, distinguishing them from the macro-enabled XLSM format.
How to open an XLSX file
As an industry-standard open format, XLSX is supported natively by Microsoft Excel, Apple Numbers, and Corel Quattro Pro. Cross-platform open-source suites like LibreOffice and Apache OpenOffice provide full read/write capabilities. Cloud-based platforms, including Google Sheets and Microsoft Excel for the Web, allow direct editing in a browser without local software installation.
XLSX Technical Info
- Full Name
- Excel Open XML Spreadsheet
- Developed By
- Microsoft
- Initial Release
- 2007
- MIME Type
- application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
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Why RunConvert
The fastest way to convert any file
Purpose-built for speed, privacy, and breadth of format support.
Convert XLS to XLSX in seconds
Every XLS to XLSX conversion runs on our servers, so your device stays fast and the output quality stays intact.
Fast, cloud-powered
No queue, no waiting. Files are processed on high-performance servers and returned in seconds, even for large files.
Secure & private
Encrypted in transit and never shared with anyone. Uploads are erased the moment your job completes, and results shortly after.
Free - no account needed
Convert without creating an account - no credit card, no trial clock. Sign in only if you want history and higher daily limits.
Developer API
Convert XLS to XLSX via API
Automate XLS to XLSX conversions in three steps: create a job, upload your file, then poll for the result.
# 1. Create job
curl -X POST https://api.runconvert.com/v3/jobs \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"tag": "xls-to-xlsx",
"tasks": {
"upload-file": {
"operation": "import/upload"
},
"convert": {
"operation": "convert",
"input": "upload-file",
"output_format": "xlsx"
},
"export-result": {
"operation": "export/url",
"input": "convert"
}
}
}'
# 2. Upload your file (use upload_url from the response)
curl -X PUT "$UPLOAD_URL" --upload-file input.xls
# 3. Poll for result
curl https://api.runconvert.com/v3/jobs/$JOB_ID?include=tasks \
-H "Authorization: Bearer YOUR_API_KEY"Replace YOUR_API_KEY with your RunConvert API key. Get your free API key at runconvert.com/api.
FAQ
Frequently asked questions
Common questions about converting XLS to XLSX with RunConvert.
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