Do you mean to ask if it is used in the English language? The answer is that it is.
Tininess means the property of being very small in size. The pronunciation (using the International Phonetic Alphabet) looks like this: /ˈtʌɪninəs/. Other pronunciations may exist. There are three syllables with the stress on the first syllable: TINE-y-ness (to use an unregulated pronunciation system).
If you want to learn more about the International Phonetic Alphabet, you can find a guide here: International Phonetic Alphabet and Phonemic Alphabets