XLS to XLSX — Format Comparison & Online Converter
Fast, instant XLS to XLSX conversion. No signup required. Just drop your .xls file and get .xlsx in seconds.
Batch Settings
Some metadata may not survive
Your XLS file may contain OLE properties metadata. XLSX has limited or no support for these metadata types. Location data (GPS), camera settings, and color profiles may be stripped during conversion.
古いExcelファイル（.xls）を開こうとして、「このファイルは古い形式です」という警告に出くわした経験はないでしょうか。Office 2003以前の形式であるXLSは、今や多くの環境で扱いにくくなっています。特に複数人での共同作業や、クラウドサービスへのアップロード時に問題が起きがちです。XLSXへ変換することで、ファイルサイズが軽くなり、数式やセルの書式も引き継がれます。難しい操作は不要で、ファイルをアップロードするだけで変換が完了します。
- 同人誌の売上管理表をクラウド共有用に変換
- 取引先への見積書・請求書を最新形式で送付
- 縦書き設定や禁則処理を保持したまま社内資料を更新
日本では公官庁や金融機関が配布する申請用Excelファイルに今もXLS形式が使われているケースがあります。XLSXへ変換する際、全角文字や縦書きセルの表示が崩れないか、変換後に一度確認することをおすすめします。
About XLS to XLSX Conversion
XLS (introduced 1987) and XLSX (introduced 2006) are both spreadsheet formats, but they differ in important ways. XLS is the legacy Excel format (pre-2007) — still encountered in business workflows. XLSX is Microsoft Excel's modern format supporting formulas, charts, and multiple sheets.
Full Name: XLS uses Microsoft Excel Legacy, while XLSX uses Microsoft Excel Spreadsheet. Compression: XLS uses None (uncompressed), while XLSX uses Lossless. Typical File Size: XLS uses 50 KB–50 MB, while XLSX uses 50 KB–50 MB.
When you convert XLS to XLSX, the goal is to upgrade to a modern format. Converting XLS to XLSX maintains high quality with CocoConvert's optimised encoder settings. Understanding these technical differences helps you choose the right format for your workflow.
Your XLS file is decoded and re-encoded as XLSX. The conversion involves 4 steps: (1) your xls file is uploaded and the format is validated, (2) the file content is decoded into its raw representation, (3) the data is re-encoded in xlsx format with optimal settings, (4) the converted file is ready for download.
CocoConvert's converter handles the entire pipeline server-side using FFmpeg, Sharp, and qpdf — battle-tested libraries used by streaming platforms and enterprise tools. Files are encrypted in transit and deleted within 24 hours.
This conversion is ideal when you You need maximum device and software compatibility. For the opposite direction, CocoConvert also supports XLSX to XLS conversion.
How to Convert XLS to XLSX
- 1
Upload .xls file
Select your XLS file by dragging it to the upload zone or using the file picker. Batch upload is available for multiple files.
- 2
Choose .xlsx
Set XLSX as the output format. The converter uses optimal settings based on the XLS→XLSX conversion profile.
- 3
Convert
The server-side engine decodes your XLS file and re-encodes it as XLSX. Processing time depends on file size and complexity.
- 4
Download result
Grab your converted .xlsx file. Multiple output files can be downloaded together.
What Happens When You Convert XLS to XLSX
Your XLS file is decoded and re-encoded as XLSX.
Your XLS file is uploaded and the format is validated
The file content is decoded into its raw representation
The data is re-encoded in XLSX format with optimal settings
The converted file is ready for download
XLS vs XLSX — Detailed Comparison
| Feature | .XLS | .XLSX |
|---|---|---|
| Full Name | Microsoft Excel Legacy | Microsoft Excel Spreadsheet |
| Compression | None (uncompressed) | Lossless |
| Typical File Size | 50 KB–50 MB | 50 KB–50 MB |
| Platform Support | Universal | Universal |
| Browser Support | none | none |
| Year Created | 1987 | 2006 |
| Open Standard | No | Yes |
Should You Convert XLS to XLSX?
When to Convert
- ✓You need maximum device and software compatibility
Common Mistakes When Converting XLS to XLSX
"XLSX will be smaller than my XLS file"
XLSX uses lossless compression, so the output file is often larger than a lossy XLS. If you need a small file, XLSX may not be the right choice.
Frequently Asked Questions
What is the difference between XLS and XLSX?
XLS is the legacy Excel format (pre-2007) — still encountered in business workflows. XLSX is Microsoft Excel's modern format supporting formulas, charts, and multiple sheets. Full Name: XLS uses Microsoft Excel Legacy, while XLSX uses Microsoft Excel Spreadsheet. Compression: XLS uses None (uncompressed), while XLSX uses Lossless. Typical File Size: XLS uses 50 KB–50 MB, while XLSX uses 50 KB–50 MB.
Does XLS to XLSX conversion affect quality?
Converting XLS to XLSX maintains high quality with CocoConvert's optimised encoder settings.
Which format has better compression, XLS or XLSX?
XLS uses none compression. XLSX uses lossless compression. The better choice depends on whether you prioritize file size or quality.
How long does XLS to XLSX conversion take?
Most conversions finish in seconds. Larger files or complex spreadsheet content may take 10–30 seconds. CocoConvert processes files in parallel for batch jobs.
Is XLS or XLSX better for long-term storage?
XLSX is better for archival since it preserves all original data.
Versions are pinned in our worker Dockerfile and re-built via CI on every change.