You can't directly adjust the font size in QuickBooks Online (QBO), but you can change it in your browser settings for easier readability.
Press the Ctrl key and either the + or - keys or hold the Ctrl key while scrolling your mouse wheel up or down. You can also set a default size in your browser's settings, but please note that these changes will only affect specific parts of QuickBooks, such as the list of options accessible through the Gear icon.

To modify it, here’s how:
Google Chrome:
- Click the Ellipsis (three dots) in the upper right corner.
- Select Settings.
- Under Appearance, adjust the Font size and Page zoom settings.
Mozilla Firefox:
- Click the Hamburger icon.
- Choose Settings.
- Update the font size as needed.
Microsoft Edge:
- Click the Ellipsis in the upper-right corner.
- Click Settings.
- Scroll down to Appearance.
- Adjust the font size according to your preference.
If you wish to modify the font size in your sales forms, you can utilize the Custom form style option. Follow the steps for guidance:
- Click on the Gear icon and select Custom form styles.
- Under New style, choose the sales form you wish to modify.
- Click on Select a different font and choose your desired font.
- Once finished, click Done to save the changes.

Adjust your QBO set up to fit your workflow preferences. Refer to this article for help: Edit company settings.
The Community is always here to support you, from adjusting QuickBooks settings to handling sales forms. Know that we're eager to assist and guide you with any QBO concerns you have.