Office for Mac Issues

How to Fix PowerPoint Text Boxes Changing Font Size Unexpectedly on Mac

Phi Hung Vo Sep 28, 2026 869 views

Question details

The user needs to fix an issue in PowerPoint for Mac where specific existing text boxes unexpectedly change font sizes on their own and display a blank or incorrect font-size value.

How to Fix PowerPoint Text Boxes Changing Font Size Unexpectedly on Mac

Product: Microsoft PowerPoint for Mac
Device & OS: macOS 14.5
Scenario: Editing an existing presentation where specific text boxes become corrupted, lose their formatting, and display a blank font size field, while new slides remain unaffected.
Observed behavior: The font size inside specific existing text boxes changes unexpectedly. When selecting the text box, the font-size field in the ribbon appears completely blank or displays an incorrect value.

Before you start

Before proceeding with troubleshooting, duplicate your presentation file in Finder to ensure you have a safe backup while testing fixes on the corrupted slides.

Solution 1Recommended

Recreate Corrupted Text Boxes Using Unformatted Text

Since the issue is isolated to specific text boxes within an existing presentation, the internal formatting of those shapes is likely corrupted. Replacing them is the most effective fix.

When an individual text box's XML formatting breaks, PowerPoint struggles to render the assigned text size, resulting in a blank font-size field. Rebuilding the text box and stripping the old formatting resolves this.

Copy the original text

Double-click inside the corrupted text box, select all the text, and press Cmd + C to copy it. Do not select or copy the outer bounding box itself.

Insert a new text box

Go to the 'Insert' tab on the PowerPoint ribbon, click 'Text Box', and click on an empty area of your slide to draw a new text box.

Paste without formatting

Click inside the newly created text box and press Cmd + Shift + V (or right-click and select 'Keep Text Only'). This pastes the text without bringing over the corrupted formatting.

Delete the old text box

Click the outer edge of the original, malfunctioning text box so the border becomes a solid line, then press the Delete key to remove it.

Recreate Corrupted Text Boxes Using Unformatted Text

Pro Tip: If you are pasting a large amount of text, you can first paste it into a plain-text application like TextEdit (set to Plain Text mode) to completely scrub any hidden formatting before moving it back to PowerPoint.

Solution 2

Update macOS and Microsoft Office

Software bugs, including text rendering and user interface glitches, are frequently patched in system and application updates.

Solution 3

Repair or Reinstall PowerPoint for Mac

If updating does not resolve the blank font size field and the issue spreads to new presentations, your Office installation files may require a clean reinstallation.

Free Microsoft Office alternative

Experience Stable Presentations with WPS Presentation

If PowerPoint for Mac frequently corrupts your text boxes or struggles with unexpected formatting bugs, consider migrating to WPS Office. It provides a lightweight, highly compatible, and free alternative with a familiar user interface, ensuring your slides maintain their intended layout and font sizes without unexpected glitches.

1. Download WPS Office: Visit the official WPS website and download the free WPS Office installer designed specifically for macOS.
2. Install the Application: Run the downloaded installer and follow the simple on-screen prompts to set up WPS Office on your Mac.
3. Open Your Presentation: Launch WPS Presentation, open your existing .pptx files, and enjoy a stable editing experience without worrying about font-size corruption.

Completely free and lightweight presentation softwareSeamlessly compatible with Microsoft PowerPoint (.pptx) formatsFamiliar user interface requires zero learning curveStable text formatting engine prevents unexpected resizing bugs

microsoft office alternative - wps office

Frequently Asked Questions

Why does the font size field go blank in PowerPoint for Mac?

A blank font size field typically indicates either that the selected text box contains text of multiple different sizes, or that the internal formatting data for that specific shape has become corrupted. If selecting all the text and manually typing a new size does not resolve it, the text box must be recreated.

How do I set the default text box font size in PowerPoint for Mac?

To set a standard format, insert a new text box on a slide, adjust the font style and size to your preferred default settings, right-click the outer edge of the text box, and select 'Set as Default Text Box'.

Will restarting my Mac fix unexpected font size changes in PowerPoint?

Restarting your Mac clears temporary system cache and can resolve minor graphical rendering glitches. However, if the issue is embedded in a specific presentation's corrupted text boxes, restarting will not fix the broken formatting. You will need to recreate the affected text boxes.

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