The Underbust measurement isn’t as famous as the bust or waist, which is sort of a shame, I feel. The Underbust is the measurement of the ribcage, directly below the bust. Aside from being a crucial measurement for making modern bras fit, it’s important for underbust style corsets, some styles of later-era long line corsets, regency fashion, and even modern baby-doll styles. Here’s how to take the measurement accurately….
This is another measurement that is difficult, if not impossible, to accurately take without help. With the measuree’s arms out to the sides, the measuring tape should be run around the ribcage, directly below the bust, and level with the ground. This doesn’t necessarily translate to “follow the bra band” – they rarely seem to stay level. Here’s a tricky thing: if you are over a B cup and over 30 (27 for a D), you might find that the amount of ribcage between your bust and your waist has decreased a little over time. In a perfect world, you want to take this measurement up by where the breasts, erm, bloom out from the body, rather than where they eventually flop to. In other words, if they’re saggy, wear a supportive bra with a band that doesn’t cut in to the body unduly. (For the record, your boobs should end up about midway between shoulder and elbow level. If they’re lower, you need to adjust your bra straps. If they’re higher, no one really believes you.)
Once the tape is situated properly, the measuree should lower her arms, stand in her normal posture, and inhale normally. (Opera singers should inhale deeply.) This is the proper underbust measurement.
There are circumstances where it’s useful to know how much of the underbust measurement is in front of the body, and how much is to the back. (Swimmers, in particular, will build a lot of muscle across the back here.)
You can take the underbust measurement with the tape at the side of the body, directly below the armpit.Wrap the tape around the back of the body, past the sideline, and around the front. Make sure the tape is level, and inhale as before. (In this case, lowering the arms makes it difficult to read the tape…) Read the measurement at the sideline of the body opposite where you started. This is the Back Underbust measurement. Read the full measurement, and subtract the back underbust from it. The result is the Front Underbust measurement.