One of the important things to learn when learning English is how to guess at the pronunciation of a new word.
This is one reason we spend so much time on KK and phonics.
But there are other equally-important rules.
If a word has a double consonant (two of the same consonant) after a single vowel sound that has long and short forms, then the vowel sound will usually be short.
If a word has a single consonant after a vowel sound that has long and short forms (if not already covered by other rules,) then the vowel sound will usually be long.
“Filed” is /faɪld/. “Filled” is /fɪld/.
“Diner” is / ̀daɪnɚ/. “Dinner” is / ̀dɪnɚ/.
“Loped” is /lopt/. “Lopped” is /lɑpt/.
“Mated” is / ̀metɪd/. “Matted” is / ̀mætɪd/.
“Cuter” is / ̀kjutɚ/. “Cutter” is / ̀kʌtɚ/.