This is a QuickBooks Desktop setting, not a QuickBooks Online one. Go to Edit > Preferences > Desktop View, open the font settings from that tab, pick which screen element you want to change (lists, registers, labels), choose a size in the standard Windows font picker, and save. Here's the full walkthrough, and what to do instead if you're on QuickBooks Online.
1. Open Preferences. From the Edit menu, select Preferences.
2. Select Desktop View. Click it in the left-hand icon list, then stay on the My Preferences tab.
3. Open the font settings. Look for the Fonts & Colors control on this tab. It opens a separate dialog rather than changing anything inline.
4. Pick the screen element you want to resize. You can usually set the size separately for different areas, register text, labels, supporting text, rather than one global size for everything in the program.
5. Choose the new size in the Windows font dialog. This opens your operating system's standard font picker; pick the size (and font, if you want) and confirm.
6. Save and close out of Preferences. Click OK on each open dialog to apply it. You may need to close and reopen the window you were viewing for the new size to show up everywhere.
The instinct is to look for font settings somewhere obviously visual, a display tab, a theme setting, and Desktop View is a reasonable first guess, but the actual control lives a level deeper inside it, not as its own top-level preferences category. It's an easy thing to miss on a first pass through the menu.
The bigger mix-up isn't where the setting lives, it's which font people are actually trying to change. Someone searching for this because an invoice looks wrong to a customer needs a completely different setting, not this one. The display font only affects how QuickBooks looks to the person using it; it has no effect on what a customer sees on a printed or emailed invoice.
Invoice and estimate templates stay in sync with your current branding, logo, colors, fonts, across every QuickBooks company file a business runs, instead of someone manually updating each template whenever a rebrand happens.
For businesses that need a specific layout QuickBooks's template editor can't produce, documents get generated in a separate tool and attached to the QuickBooks transaction automatically, instead of fighting the built-in template editor.
Tell us whether it's a display issue, a branding issue, or a layout QuickBooks just can't do, and we'll tell you what's actually fixable and how.
Tell us whether it's the screen you're staring at all day or a document a customer actually sees, and we'll tell you what's worth fixing and how. Display settings are a small example; the same offer stands for anything manual in your business, QuickBooks or otherwise.
Let's talk →There's no in-app setting for this in QuickBooks Online. Font size on screen is controlled by your browser, not QuickBooks: use your browser's zoom (Ctrl and + or - on Windows, Cmd and + or - on Mac) to make everything on the page larger, QuickBooks included.
That's a different setting from the one covered above. Invoice fonts are controlled through Custom Form Styles: go to the gear icon, then Custom Form Styles, open or create a style, and change the font under the style's design options. This affects what the customer sees on the invoice, not how QuickBooks looks on your own screen.
It varies by which Custom Form Style template you've picked; QuickBooks ships several built-in styles with different default fonts, and you can override the font on any of them from that style's design settings.