What are the default margin (in inches) and font title and text size of this LaTeX document template I found? I can't seem to find a certain answer.
Here's the link to the template: https://www.overleaf.com/articles/acceleration-in-fixed-point-iteration-and-nesterov-s-gradient-method/pksgtcxdcffq
If I understand your setup correctly, you're using the article document class. This is one of the most common general purpose LaTeX document classes.
Assuming your TeX distribution is fully up to date, you're using v. 1.4n (2021/10/04) of article.cls.
Since you do not appear to load this document class with any particular options, the default font family is Computer Modern and the default document font size is 10pt.
The default margin sizes depend in part on the size of the printer paper you employ. The two most common paper sizes for general document typesetting are letterpaper (aka "US Letter", 11in x 8.5in or 795.0pt x 614.3pt; used mainly (exclusively?) in North America) and a4paper (aka "A4 paper", 297mm x 210mm or 845.05pt x 597.51pt; used for printers just about everywhere else in the world).
Your TeX distribution is likely set up to choose one or the other of these two options as the default paper size. Don't assume, though, that just because your computer and any attached printer may be based somehwere in Europe, say, that the option a4paper is in effect by default for your TeX distribution. I, for one, am based in Europe, but I've deliberately chosen letterpaper as the default paper size, mainly because the overwhelming majority of my scientific collaborators happen to be based in North America. (In case you're curious: I'm an economist. Not having to re-format LaTeX papers that we email each other back and forth across the Atlantic is a big time saver...)
The file article.cls also defines sizes for a5paper, b5paper, legalpaper, and executivepaper. If you load a package such as geometry, many more default paper sizes are defined for you to choose from.
Assuming you're using the (basic) 10pt font size, we could next look into size10.clo -- I think "clo" stands for "class options" -- for further information about margins.
Unfortunately, I cannot in good conscience recommend you spend much time going through size10.clo (or, for that matter, size11.clo or size12.clo). They're chock-full of information, but they aren't exactly easy to parse.
Suffice it to say that the default value of \textwidth (the width of the text block) is 345pt -- this works out to 4.774in, or 12.125cm -- if either letterpaper or a4paper is in effect. You may verify this directly, by the way, by executing \the\textwidth somewhere in your test document.
The default value of \textheight may be calculated from a knowledge of \paperheight and the default settings of \topmargin and \bottommargin. Long story short: as long as the geometry package is not loaded, the parameter \textheight works out to 550.0pt (aka 7.61in or 19.33cm) if letterpaper is in effect, and to 598.0pt (aka 21.02cm or 8.275in) if the option a4paper is in effect.
Thus, even though \textwidth is the same by default regardless of whether letterpaper or a4paper is in effect, this is not the case for \textheight: this parameter is ca 1.8cm larger if a4paper is in use.
Unless the twoside document class option has been chosen (which isn't the case for the template document), the horizontal margins are symmetric. Thus, assuming letterpaper is in effect (for which \paperwidth equals 8.5in), the left and right hand margins can be calculated by subtracting \textwidth from \paperwidth and dividing the result by 2: 1.863in. Calculating the value of \leftmargin and \rightmargin for the case that a4paper is in effect is left as an exercise to the reader.
If you're starting to think that the exposition used in the preceding bullet points is rather convoluted, you're not alone. I, for one, would never recommend that you manipulate the LaTeX parameters that govern the margins directly. Instead, I would strongly recommend that you employ the geometry package to set the paper size and the margin widths or, equivalently, the values of \textheight and \textwidth.
Happy (La)TeXing!
