Why Excel Uses Little CPU When Opening Large Workbooks
Question details
The user wants to understand why Excel uses little CPU when opening a large workbook and how to improve performance.
- Product
- Microsoft Excel for Microsoft 365, 64-bit
- Device & OS
- not provided
- Scenario
- Opening, saving, closing, or copying a 250 MB workbook on a computer with 32 CPU cores.
- Observed behavior
- The workbook takes about eight minutes to open while overall CPU usage remains low. Safe Mode did not improve opening time, and switching to manual calculation made Excel appear unresponsive for more than 15 minutes.
Note the workbook's location and approximate opening time so you can compare tests. If Excel is currently unresponsive after changing calculation mode, allow it time to finish before making further changes.
Test the workbook on a local drive and review external links
Use this test to identify delays caused by storage access or linked workbooks.
Excel cannot use every core for every operation. A task using roughly one core on a 32-core computer can appear as only about 3% overall CPU usage; file input/output and workbook processing can also limit performance.
Copy the workbook to a fast local drive, then open it from Excel using File > Open. Compare the opening time with the original location.
When the workbook opens, go to Data > Workbook Links or Data > Edit Links, depending on your Excel version. Check whether linked sources are available and whether they need to update.
Use the link controls on the Data tab to change update behavior only if appropriate for the workbook. Break or remove a link only after confirming that the linked data is no longer needed.
Reduce workbook complexity and check calculation settings
Use this approach when the workbook itself remains slow after a local-drive test.
Open Excel Workbooks with WPS Spreadsheet
WPS Office is a free, lightweight alternative with a familiar spreadsheet interface and support for Excel formats, making it easy to move existing files into WPS Spreadsheet. It does not fix Excel's CPU usage, and performance with a large or complex workbook may vary.
Frequently Asked Questions
Why does Excel show only about 3% CPU usage on a 32-core computer?
Overall CPU usage is averaged across available processors. An operation that uses roughly one core may show about 3% overall usage, although storage delays and other limits can also affect the reading.
Can I make Excel use all CPU cores to open a workbook?
Not necessarily. Some workbook operations are single-threaded or limited by file access and workbook structure. Excel can use multiple threads for certain calculations, but that does not make every opening or closing task use all cores.
Should I switch to manual calculation to open the workbook faster?
Manual calculation can be useful for testing, but changing the setting may itself take a long time or make Excel appear unresponsive. If Excel is responsive, review the setting under File > Options > Formulas and restore Automatic when appropriate.
Where can I check for external workbook links?
In Excel, open the Data tab and look for Workbook Links or Edit Links, depending on your version. Review linked sources and update settings before changing or breaking any links.
