Convert XLS to XLSX
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Built on enterprise-grade document engines. You'll notice the difference — sharper formatting, accurate formulas, and preserved charts and merged cells that other free tools lose.
Drag & drop up to 10 files here, or click to select files.
Why Upgrade XLS to XLSX in 2026
XLS is the binary Excel format from 1997-2003. XLSX is the Open XML format Microsoft introduced in 2007 — same Excel, different container. Almost every reason to keep XLS has expired in 2026: modern Excel and every cloud spreadsheet (Google Sheets, Office 365, Numbers) treats XLSX as the canonical format, and most modern features (1M rows, dynamic arrays, conditional formatting > 3 rules, threaded comments) only work in XLSX.
Beyond capability, XLSX is roughly 30-50% smaller on disk than the equivalent XLS — it's a ZIP-compressed bundle of XML, where XLS is uncompressed binary. Backups, email attachments, and version-controlled spreadsheets all benefit. And because XLSX is open-standard XML, every modern tool (pandas, openpyxl, SheetJS, LibreOffice) can read it without proprietary code paths.
The upgrade is lossless in the vast majority of cases — XLS is a strict subset of XLSX. ExcelMaster's converter checks for the few edge cases (truncated long text, deprecated VBA APIs) and reports them upfront.
How to Convert XLS to XLSX
- 1
Drop your legacy .xls file(s)
Up to 10 files at once. The tool reads BIFF5, BIFF7, and BIFF8 — every legacy XLS format from Excel 5 (1993) onwards.
- 2
ExcelMaster parses the BIFF binary stream
XLS is a structured binary format with explicit cell, formula, formatting, and metadata records. We use a real BIFF parser (the same kind underlying Microsoft's own conversion) — not a heuristic guess.
- 3
Cells, formulas, formatting carry over verbatim
Every value, every formula, every cell style maps cleanly to its XLSX equivalent. Conditional formatting rules upgrade from the XLS 3-rule limit to XLSX's unlimited.
- 4
VBA macros transfer (output is .xlsm in that case)
If your XLS contains VBA macros, the output is .xlsm (macro-enabled XLSX) — not plain .xlsx. We preserve the original VBA modules byte-for-byte.
- 5
Long text and merged cells preserved
XLS sometimes truncates long cell content at 1,024 characters in display. ExcelMaster reads the full underlying string (up to 32,767 chars) and stores it cleanly in XLSX.
- 6
Download your modern .xlsx (or .xlsm)
The output opens in Excel 2007 onwards, Excel for Mac, Excel for the web, Google Sheets, Numbers, LibreOffice — every modern spreadsheet tool. File size is typically 30-50% smaller than the original .xls.
ExcelMaster vs Other XLS to XLSX Converters
Most converters handle the simple case. Here's where they diverge.
| Capability | ExcelMaster | CloudConvert / Convertio | Browser-only converters |
|---|---|---|---|
| Reads all BIFF versions (5/7/8) | Yes | Yes | Often BIFF8 only |
| Preserves VBA macros (XLS w/ macros → XLSM) | Yes — full VBA module copy | Yes | Often dropped silently |
| Reads truncated >1024 char cells fully | Yes | Partial | Truncated |
| Batch convert (10 files at once) | Yes — free tier | Paid plan | One at a time |
| Preserves named ranges | Yes | Yes | Lost |
Same Conversion in Code
Web UI is the fastest path; here's the equivalent for batch automation.
import pandas as pd
from pathlib import Path
for xls_path in Path('legacy/').glob('*.xls'):
# Read with xlrd (engines='xlrd' for legacy .xls)
sheets = pd.read_excel(xls_path, sheet_name=None, engine='xlrd')
out_path = xls_path.with_suffix('.xlsx')
with pd.ExcelWriter(out_path, engine='openpyxl') as writer:
for sheet_name, df in sheets.items():
df.to_excel(writer, sheet_name=sheet_name, index=False)
print(f{xls_path.name} -> {out_path.name})conversion.deepContent.xls-to-xlsx.codeSnippets.javascriptCommon XLS to XLSX Pitfalls
Macros disabled on first open
Excel 2010+ disables macros by default in .xlsm files for security. Users have to click "Enable Content" in the yellow security bar. This is by design — but it surprises users moving from .xls (where macros ran automatically).
Dates shifted by a day in older files
Excel for Mac 2008 used a 1904 date system; Windows Excel uses 1900. Converting an old Mac XLS to XLSX without the right base-date can shift every date by 4 years. ExcelMaster auto-detects the base date and adjusts.
External link references break
If your XLS has links to other XLS files (e.g., =[Q1.xls]Sheet1!A1), the converted XLSX still references the .xls files — not the converted .xlsx versions. Convert the linked files too, or use Excel's Edit Links to remap.
Add-in functions don't carry
XLS files using legacy add-ins (Solver, Analysis ToolPak from Excel 2003) reference functions by add-in name. The XLSX still works, but the add-in must be re-registered in modern Excel.
XLS to XLSX — Frequently Asked Questions
Is XLS to XLSX lossless?
In 99%+ of cases, yes. XLS is a strict subset of XLSX feature-wise. Edge cases that may need attention: external links, deprecated add-in functions, and Mac 1904-date workbooks (auto-handled).
Why is XLSX better than XLS in 2026?
1M rows (vs 65,536), unlimited conditional formatting rules (vs 3), threaded comments, dynamic arrays, smaller file size (~30-50% smaller), and native support in every modern tool from Google Sheets to pandas.
Will my macros survive the conversion?
Yes — if your XLS has macros, the output is .xlsm (not plain .xlsx) and VBA modules are copied byte-for-byte. The user opening the .xlsm will need to click "Enable Content" the first time, by Excel's security default.
Can I batch convert a folder of legacy .xls files?
On the free web tier, 10 files at a time. For unlimited batch, use the Python snippet above or our desktop add-in. The CLI version handles thousands of files in one pass.
Will the file size shrink?
Typically 30-50% smaller. XLSX is ZIP-compressed XML; XLS is uncompressed binary. A 5 MB XLS often becomes a 2-3 MB XLSX with identical content.
I get "file is corrupt" when opening the converted XLSX. What now?
Most often this means the source XLS itself was already partially corrupt. Run our XLS Repair tool first, then convert. Alternatively, the XLS may be password-protected (run XLS Unlock first).
About Us
At ExcelMaster.ai, we're a group of Excel experts, AI researchers, and engineers dedicated to addressing the challenges Excel users face. Whether it's through our free tools or premium solutions, we aim to make your experience smoother. Try our Excel Add-In, the only AI capable of automating complex formulas, VBA, and Python tasks, with an advanced understanding of your real-world Excel structures—delivering far superior accuracy compared to ChatGPT and other basic AI tools. [Click Here]
XLS to XLSX Overview
Our free tool allows you to convert Excel files into a variety of formats, offering maximum flexibility for your document conversion needs. It's fully online and compatible with multiple platforms, including Mac OS, Linux, Android, iOS, and more.
How to Convert XLS Files to XLSX
Upload Your Files: Select the Excel files you want to convert and upload them to the website.
Start Conversion: Hit the "Convert" button to initiate the process.
Download: You can immediately download your converted files
File Deletion Notice: Please note that files are automatically deleted from our servers after 24 hours, and download links become inactive after this time.
Key Advantages - XLS to XLSX
No Signup Required
Enjoy hassle-free usage with no sign-up needed. Works smoothly across platforms, including Windows, Mac, iOS, and Android.
Batch File Conversion
Easily convert multiple Excel spreadsheets in one go—upload up to 10 files at a time.
Data Privacy and Security
Your data is secured using advanced encryption methods and is never used for any other purposes. All files are permanently deleted after 24 hours.
Enterprise-Grade Output Quality
Most free converters lose fidelity on complex Excel elements — charts, conditional formatting, merged cells, formulas. ExcelMaster.ai is built on industry-standard, enterprise-grade document engines, the same class of technology used in mission-critical business workflows. The conversion looks simple — but the output quality matches premium commercial tools. Free, no compromises.
What is XLSX?
XLSX is a file format used by Microsoft Excel for spreadsheet documents, utilizing a combination of ZIP compression and XML. It allows users to store and organize data in a structured way, including features such as formulas, charts, graphs, and macros. XLSX is commonly used for data analysis, reporting, and data management, particularly when compatibility with modern Excel versions is required.
Data Loss During Conversion
When converting older Excel formats (like XLS) to XLSX, some features such as macros or certain formulas might not convert properly, leading to potential data loss.
Compatibility Issues
Some older versions of Excel do not support XLSX format, which can lead to accessibility problems for users who have not upgraded their software.
Increased File Size
XLSX files can sometimes be larger than their XLS counterparts due to the inclusion of richer data types and features, which may make file sharing more cumbersome.
Corruption Risk
There is a risk of file corruption during the conversion process, especially if the original file is large or contains complex formulas, which can render the file unusable.
What are the differences between XLSX and XLS?
File Format
XLSX is the modern file format used by Microsoft Excel, introduced with Excel 2007, and is based on the Open XML standard. In contrast, XLS is the older binary file format used by earlier versions of Excel up to 2003.
File Size
XLSX files are generally smaller in size compared to XLS files because they use Zipping compression, making it more efficient for storage and sharing.
Data Capacity
XLSX supports a significantly larger amount of data, allowing for up to 1,048,576 rows and 16,384 columns per worksheet, while XLS is limited to 65,536 rows and 256 columns.
Features and Functions
XLSX files support newer features and functions available in Excel 2007 and later versions, such as improved charting tools, Sparklines, and enhanced formulas. XLS files do not have access to these advanced features.
Try Other XLS or XLSX Conversions
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