As with present participles, sometimes we double a final consonant when making a gerund. For example, the gerund of run is running. Generally speaking, these are the rules of when to double a final consonant to form a gerund:
If a one-syllable verb ends in consonant-vowel-consonant, double the final consonant, as in strumming, cutting, blurring, and spinning.
Rule 1 is ignored if the verb ends in –w or –y as in knowing or playing.
For longer verbs that end in consonant-vowel-consonant, we only double the final consonant if the last syllable is stressed:
Stressed: omitting, referring, forgetting
Unstressed: visiting, eliciting, fidgeting