CONVERT
XLS → XLSX

Yes. The free tier accepts files up to 100 MB without registration, email capture or watermarks. Paid plans raise the size cap, enable batch conversions and provide a REST API for automation, but nothing on the free tier is quality-limited — the output is exactly the same as on any paid plan.

Yes. Standard formulas, named ranges and references transfer cleanly. Custom add-in formulas may not survive if they target Excel-specific APIs; plain arithmetic, SUMIFS, VLOOKUP, INDEX/MATCH and modern dynamic-array formulas all work.

Uploads run over HTTPS, files are processed in isolated containers, and both the source XLS and the XLSX output are auto-deleted within two hours. No account is required, file contents are never logged, and KaijuConverter does not use uploads for AI training. The paid plan adds a signable data-processing agreement for regulated workflows.

Typically 30-50% smaller. XLSX is a ZIP-compressed XML package; XLS is a binary format with historical bloat. The compression also makes XLSX faster to open and more resilient to corruption.

Most files finish in well under a minute. Small images and documents are typically ready in a few seconds; large video or audio files scale roughly with duration. Upload speed from your network is usually the dominant factor, not server time.

Yes. Pivot tables, conditional formatting, named ranges and multi-sheet structure all survive. Charts generally transfer with the same series and formatting, occasionally with minor styling differences.