What is the optimal icon size and should I use SVG?

Question

User interface

Why icons are mostly 32, 48, 64, etc. pixels? Do you try to use icons with fractional sizes of 2? Inspired by: I use icons from icons8.com, they have sizes of 50 pixels, 100 pixels. I compress to 48 pixels. - so the quality is lost, of course. Does it make sense to compress at all or use 50 pixels anyway. icons? For mobile, I plan to simply reduce them by 2 times, thus there will be clarity on retinas if png .
Say, use SVG ? On icons8, they won’t buy svg icons for me, there’s no one to draw them either and for a long time. Icon fonts - FontAwesome doesn't have the necessary icons, other free ones have even less set. Or maybe there are a lot of free svg icons somewhere?

Answer 1

if you mean viewbox for SVG, then fractional 2m is better - otherwise it may render poorly.
you can compress using SVGO, it will remove unnecessary tags from svg.
here https://thenounproject.com there are a lot of icons in svg, you can download it for free - there will be text below, but it can be easily removed in the editor.

Answer 2

"other freebies have even less set", well, you underestimate other sets. Material Design
has a pretty decent collection, and the number of smaller collections that can be used on small-to-medium projects is too large to list them in one post, someone devoted an entire article to this . Many almost free svg icons can be found on flaticon . Why almost? Their use implies the mention of the author. You can avoid this by purchasing a subscription, but the price is ridiculous, less than $ 8 per month for an annual subscription, compared to $ 20 icons8 is quite good for itself. There is also iconfinder
, the subscription is more expensive here, but there are completely free icons (although they are usually of rather low quality, IMHO) and in general there are 3-4 times more icons.

Answer 3

and should I use SVG?

Very caniuse.com/#search=svg It's not even the future, it's the present
According to frequency of use
Unclear. It depends on what, how and how to compress.
And what's the problem if there is a png icon, for example, to make svg out of it? There are online services for this and there is great software - inkscape.paint-net.ru/?id=1