I am creating a form for web, and the word Length is being again and again e.g Sleeve Length, Leg Length, Inner Leg Length. Making everything a bit too long. According to this website, the LEN is used for telecom industry and doesn't say what abbreviation can be used for Length in garment business.
As mentioned in @jejorda2's comment, if there is a common heading saying e.g. Enter your measurements, then length seems implicit, so the following should suffice:
Or maybe even:
Inner Leg (cm)
By the way, you could use tooltips over each label for a 'wordier' version e.g. "Length of ...".