I would like to know if there is a standard size I can follow when designing smiley icons.
This question is very broad but I'l try to answer it as best as I can. As already mentioned there are no "standard sizes" for icons and you should edit your question to include what you're targeting. Are you:
Creating an app for Apple?
App icon required for all apps:
180 x 180
120 x 120
152 x 152
76 x 76
App required icon for the App store:
1024 x 1024
Source: IOS Developer Library
Creating an icon to be used by Android?
So, to create an icon for different densities, you should follow the 2:3:4:6:8 scaling ratio between the five primary densities (medium, high, x-high, xx-high, and xxx-high respectively). For example, consider that the size for a launcher icon is specified to be 48x48 dp. This means the baseline (MDPI) asset is 48x48 px, and the high-density(HDPI) asset should be 1.5x the baseline at 72x72 px, and the x-high density (XHDPI) asset should be 2x the baseline at 96x96 px, and so on.
Creating an icon for the web?
You could go with some common sizes:
12 x 12
16 x 16
32 x 32
64 x 64
128 x 128
256 x 256
If you are thinking of a
As stated though there is not a master standard size but I would suggest reading an excellent post called "Finger-Friendly Design: Ideal Mobile Touchscreen Target Sizes" that talks about size and finger functionality:
An MIT Touch Lab study of Human Fingertips to investigate the Mechanics of Tactile Sense found that the average width of the index finger is 1.6 to 2 cm (16 – 20 mm) for most adults. This converts to 45 – 57 pixels, which is wider than what most mobile guidelines suggest.
If you're looking for other ways to use an icon within a font you could always use something like Iconmoon which are considered icon fonts. If you want to know more about icon fonts we do have other questions. Just looking through the premium section they have some that may help you:
So additional help in regards to icon fonts:
As @pute said there is not such thing like "standard size", but you have to use multiple of 4px and any size beyond 16x16 or 96x96 usually have no utility at all. Is up to you to chose one taking into account this reasonably sizes