How would you know if its short or long vowel?

Answer 1

when 2 vowels go walking the first does the talking ,meaning the first one says its name,also silent e at the end of a word makes the vowel in the word say its name

Answer 2

A short vowel is typically pronounced with a brief, crisp sound such as /a/ in "bat." A long vowel is pronounced with a drawn-out sound, usually the sound of the letter itself, such as /aɪ/ in "like." The length of the vowel sound is often determined by the presence of a silent "e" or a vowel combination.