There are different ways to write a cinquain. Normally, I use a syllable count which is:
Line 1: 2 syllables
Line 2: 4 syllables
Line 3: 6 syllables
Line 4: 8 syllables
Line 5: 2 syllables
Total syllable count is 22.
Adelaide Crapsey is credited for developing the American version of the 5-line cinquain (pronounced sincain although this depends on which dictionary you consult as some say the second part should be pronounced keyn, kein or ken.)
Source: cinquain.org
The problem with counting syllables is the resulting poem can sound contrived. I consider this part of the challenge.
In addition, not everyone says a word in the same way. The word caramel is a perfect example. I pronounce it with two syllables; others use three syllables. Since both pronunciations of caramel are acceptable, poets could use either syllable count depending on their preference. When in doubt, I recommend consulting a dictionary.
Cinquains that use a word count instead of a syllable count are also known as didactic cinquains. Even though I will not be discussing this type of cinquain there are plenty of examples that can be found elsewhere on the internet.
Cinquain And Other Poetry Forms