Whats is default font and size of wordpress

There is none. Everything depends on the settings in the current theme’s style sheet.

For entry it just says:
.entry {text-align: justify;
font-size: 1.10em;
color: #02171d}

So there is no any font defined … arial works pretty much but its a little bigger than it needs to be

That’s weird. I suppose your visitor’s browsers will turn to their default font, which is often Times New Roman I’m afraid.