From coloradoweddings.com:
Choose the length of your veil. There are six type of veil. Shoulder length (45”), waist length (54”), hip length (72”), floor length (108”), train length (126”), and cathedral length (144”). The shoulder and waist length veil are generally used for gowns without a train and will enhance any detailing at or around the waist of the gown.
The hip length veil can be worn with any full length gown. It falls right at the fingertips of the bride if her hands are at her side and is used for formal and semi-formal weddings.
The floor, train, and cathedral length veil should only be worn with a chapel or cathedral length gown. The veil will extend onto the floor at least six inches past the train for a very dramatic look. Keep in mind that chapel and cathedral length veils can be difficult to maneuver.
A little tip, if you are small, don’t choose a veil that swamps you, such as a high bouffant veil. It will only make you look smaller.