Here's why:
* The vowel sound "a" in "laugh" can be short or long. In some dialects, the "a" is pronounced like the "a" in "cat" (short), while in others it's pronounced like the "a" in "father" (long).
* The "gh" at the end of "laugh" is silent. This means it doesn't contribute to the length of the word.
* The length of the word "laugh" can vary depending on the situation. You might say "laugh" quickly in a casual conversation, or you might draw it out if you're emphasizing the word.
So, the answer to your question is it depends.