Yeah some people prefer to use 100% for many reasons (you can google the benefits if interested), but while the 62% makes it easy to add rem’s, in some situations it’s still better to manage other parts of the code with 100%. Either way works fine, some developers prefer 100% and some 62%.
If you need to find the rem just use something like this – https://offroadcode.com/prototypes/rem-calculator/ which will give you the size you need in less than a second. I have it bookmarked so it’s easy to get to.