Users DO change font size
Evan Minto wrote a great article showing the Internet Archive has tested the actual root font-size set by their visitors, and the result shows a lot of people still change the default one: Pixels vs. Ems: Users DO Change Font Size.
we found that the answer is 3.08% of our users. That’s a pretty big number, higher than most counts of the market share of browsers like Internet Explorer, Edge, or Opera Mini.
I've said it before, several times:
- in my talk at Paris Web 2013 (in french): Un petit pas pour l’em, un grand pas pour le Web
- in a post in 2016: People don't change the default 16px font size in their browser
But people still often tell me I'm wrong, it's an edge case not worth taking into account, and using
px units everywhere is fine.
It's nice to see a renowned organization like Internet Archive work on this topic and come to the same conclusions.
Speaking of conclusions, I very much like the one of Evan Minto's article:
If 2 to 3% (or more!) of your users are relying on a custom font size, you should know that so you can either support that user preference or make a conscious decision to not support it. Doing anything less is frankly irresponsible, especially considering that users with larger font sizes may be using those sizes to compensate for visual disabilities.