In Morse code, all timings are referenced off a dit length, which depends upon the words per minute (wpm) you're trying to send. The standard word is PARIS and the math works out to
ditLength = 1200 / wpm;
So, at 5 wpm, you'd be able to send the word PARIS 5 times, which is really slow. (Continents drift faster than that.) Based on that, you get:
#define DITLENGTH (1200/wpm)
#define ELEMENTSPACE (DITLENGTH)
#define LETTERSPACE (DITLENGTH * 3)
#define WORDSPACE (DITLENGTH * 7)
Now, if you change the wpm speed, all of the related spacing changes with it. Note that this is for "standard" Morse code. Farnsoworth encoding takes a little more calculating. You could also use these definitions using the const keyword instead to define variables.