To ensure your prom or wedding dress fits perfectly, especially when shopping online, the key is accurate measurements, specifically the "hollow-to-hem" length. This measurement determines the overall length of your gown and is the distance from the hollow point between your collarbones (or the dip at the base of your neck) straight down to the floor. It is crucial to measure while wearing the exact shoes or heels you plan to wear, or account for their height, so the dress isn't too short. Always use a flexible tape measure and ask a friend for help, as measuring yourself can lead to inaccurate results.

Beyond length, remember to measure the fullest parts of your bust, waist, and hips, noting that formal dresses often run smaller than standard clothing, so you may need to size up.