This guide is intended to describe how best to use fonts with Rainmeter. There are two ways fonts might be made available to a skin. First, you might just use the fonts that come installed with Windows, and second, you might want to include custom fonts with your skin.
Custom fonts can be obtained a bunch of different places, but some of the more popular are:
There is one other external tool that can be VERY useful in managing and using custom fonts in Rainmeter. Get the dp4 Font Viewer utility. You will find it a great help in both identifying font "face" names for your skin, and in knowing what "weights" and "typography" your font(s) support. You can go to http://us.fontviewer.de/Download/ to download either a .exe installer or a .zip "portable" version of the tool.
Making your custom fonts available to your skin
All you need to do is place any font .otf or .ttf file(s) in your @Resources\Fonts folder. When the skin is loaded, the fonts in that folder will automatically be visible to your skin.
If you are not familiar what @Resources is, or where the folder should be, please take a minute to review that link above.
Using your font in your String meters
Choosing the font FACE
This option will define the font "Preferred Family Name" or "Family Name". Font families are structured in a couple of different ways, but the simplest way to get this is to double click the font .otf or .ttf file in Windows Explorer, and get the name from the top left of the Windows Font Viewer dialog that will open.
With some fonts, there may be weights like "SemiBold" or other attributes like "Condensed" appended to the font Family name shown in Window Font Viewer. Don't be too concerned about that, as Rainmeter will figure out that a font Family name like "Fira Sans SemiBold" is a part of the Preferred Family of "Fira Sans", and all Fira Sans fonts in @Resources\Fonts will be considered when other font attribute options are used.
Setting the font SIZE
This simply sets the font size in points.
Setting the font COLOR
This will set the font color, using the standard RRR,GGG,BBB,AAA RGB or RRGGBBAA Hex forms of the color codes in Rainmeter.
Setting the font WEIGHT
This will set the font weight. What works here is dependent on what weights are supported by your font Family. It is certain that 400 (Regular / Normal) will work and is the default, and that even if not supported by the font, 700 (Bold) will be simulated by Rainmeter. Other weights depend on the font supporting them.
It's important to remember that the actual file name of the .otf or .ttf file doesn't mean a thing in this context. Here is a list of the standard weights and common names that fonts use, but nothing says any font author has to follow this. Certainly not in the names of the actual font files, and not even in the SubFamily names that they use internally. That is where our external dp4 Font Viewer tool will be useful, and we will get to that in a minute.
One thing to note is that you can't mess this up really. If you specify a weight that is NOT supported by the font, it will use the nearest weight that IS supported, rounding down below 500 and rounding up at 500 and above. So in a sense, if you ask for "100", you are in effect saying "use the lightest weight available". if you ask for "500" you are in effect saying "use the nearest weight bolder than normal available".100 - Thin (Hairline)
200 - Extra Light (Ultra Light)
300 - Light
400 - Regular (Normal)
500 - Medium
600 - Semi Bold (Demi Bold)
700 - Bold
800 - Extra Bold (Ultra Bold)
900 - Black (Heavy)
950 - Extra Black (Ultra Black)
Using dp4 Font Viewer
Load this utility, then use the browse / folder button at the top left go to the folder containing your font(s). They will all be listed in the panel on the left.
Then you can check the box labeled "Weight class" and select any of the weights listed in the pull-down menu. Any font .otf or .ttf files that supports the selected weight will then be listed. If there isn't one, that weight won't work with that particular font family.
In this case, our Fira Sans font Family supports a weight of "Thin", and we know we can use FontWeight=100 in our String meter.
There will be lots of interesting and important information in the right panel for your font, in particular you should note any "License" information, to be sure you can legally distribute this font with your skin.
Extra credit: Typography
If you want to see what Typography values are supported by your font, the dp4 Font Viewer is one of the best (and almost only) ways to find out what your font supports. Select the "Glyph substitution" button at the bottom right, and a list of all Typography features your font has will be listed. Then you can use the information found at InlineSetting Typography to find the codes you need to use in the meter.
I hope this is of some help with using fonts.