Last week I introduced some basic concepts of corset fitting. While the lacing allows for a lot of flexibility in fitting a corset, of course, there's much more to it. I'm going to continue the lesson, going into greater detail with things like bust fit and vertical measurements.
General Bust Fit
Unlike bras, corsets have no cup or band sizing, which can make them a lot more flexible for fitting a bust. Underbust corsets stop at about bra band level and should ideally only affect the bust by affecting your posture, so if you're looking at bust fit, that probably means you're in overbust territory. It's hard to know if an overbust corset will fit without trying it on, so when you do, here's what you should look for. The fullest part of your breasts should settle into the fullness of the bust area of the corset. The top of the cup shape (on a sweetheart style corset, which has a contoured bust) should lay flush against the top of your breast, neither cutting in (creating a quad-boob) nor gapping. The bottom of the bust curve should support your breasts.
Small & Large Busts
If you're small busted or asymmetric, I tend to find Victorian-style semi-flat fronts easier to fit. If you're particularly full busted, make sure the "diameter" of the cup is sufficient... the vertical space of the cup is sort of equivalent to the width of an underwire spring, but luckily less specific. Still, I find that a too-small bust on a busty girl will push down the apex and cause overflow. A longer vertical space for the bust will also keep from creating a chin-rest out of a full bust. (I also have a prior article that's specifically about finding the right fit of corset for your body type.)
Bust Coverage
Lastly, regarding coverage for the bust, make sure to test what happens when you raise your arms! In a flat-front cut, a neckline at roughly nipple level is called a midbust and tends to be historically appropriate... but perhaps less so for day to day life. Modern cut overbusts should provide a comfortable level of coverage at the nipples and center front without pushing into the underarm... but that brings us to the issue of vertical measurements.
Vertical Measurements
When gauging size for off-the-rack corsets, a lot of people go off of continuous vertical measurements such as busk length or princess line. I find this method insufficient because it leaves out a hugely important piece of information: the waist level within that measurement. Two people may have a similar underbust to lap measurement but opposite fit problems.
Here's an example. Let's say the underbust to lap measurement of a corset is 10". Person A is tall, with a high waist line, perhaps full busted. It's 6" from the waist down to the lap, 4" up to their underbust. Person B is long waisted, wears their corsets low on their waistline. It's 4.5" down to their lap, and 5.5" up to underbust. On person A, an underbust might give inadequate hip and low-stomach support, but push into the bottom of the breasts. On person B, the exact same corset might make it hard to sit comfortably, but leave part of the rib cage exposed. So when communicating with a corsetiere, I recommend providing these verticals as separate measurements rather than using a continuous one.
Princess Line Length
So. What are you looking for with these vertical measurements? You want them to correspond with your preferred level of support and mobility. (This might be a good time to brush up on A Corset Family Tree, Abridged.) Shorter hip and rib measurements will give a greater range of motion. Longer measurements provide more shaping and support. As in the above examples, you can probably guess that you don't want the length to cut into either your thighs (test this sitting down), or push into your breasts or underarm.
Center Front Length
With the right shaping, the length at the center can be significantly longer at either end, though at a certain point you can lose support and the busk will stand away from the body. This diminishes the support of the lower stomach and hips.
Bonus Section: Comfort
At the end of the day, no matter how it looks, corset comfort is critical to fit. If it puts undue pressure on your ribs, that's a fit issue. If you are hunching your shoulders forward because it fights your natural posture, that's a fit issue. If you prefer to lace tightly enough that your corset cuts into your softness a bit, that's a valid choice. Conversely, be wary of lacing your corsets too loosely, as this can cause chafing. Better to have a corset with a milder waist reduction and rib shaping than wear your corset so loose it can slide around on your body.
In a custom fitting, please remember than a corsetiere only knows what they see, and not what you feel. Be really communicative about everything you experience in the corset, but you probably don't need to repeat yourself... your corsetiere should be writing on your mockup and/or taking notes on a separate sheet throughout the fitting.
Do you have any other questions about what fit looks or feels like in a corset? As I said last week, when it comes to corsets, one never stops learning about fit, but I hope I've given you a starting point help you in your corset shopping!