Hey everyone! This post has been updated (updates in italics) with regards to the questions being asked! Also thanks so much for your questions because they bring to light things that I forgot to mention and should have.
I used to think this wasn’t that important, but it is. Picking the right size can determine how many adjustments and alterations you’re going to have to make. You will probably have to make many anyway, but this can remove a good chunk. So you need to pick the correct size. Think of this in terms of altering your clothes. It’s just as hard to alter something that is way too big – like 3 sizes too big – as it is impossible to alter something that is 3 sizes too small. Picking the pattern size that is closest to you is much easier to alter than picking one that is 2 or 3 sizes too big or small for you.
For my part, I use my upper bust measurement, waist and hip. The upper bust measurement in particular is a good measurement to go by when picking a bodice because it will insure that you pick the correct shoulder, neck and sleeve arrangement for your body. You would pick this measurement in lieu of your full bust measurement for your bust – now that was a mouthful! This, if you don’t know, is the hardest place on the body to fit. Why? Because if you think of it you are trying to fit four moving tubes – your neck, shoulders, arms and upper bust. All of these tubes have different wearing ease amounts and they all play in tandem with each other. The second place on the body that is hardest to fit – the legs and torso. You’ve got three tubes there and that’s why pants are such a pain to fit. The upper bust measurement works out well too because it removes the headache of figuring out which cup size the pattern was drafted for. Instead, you pick the upper bust measurement for the bust and either do a full bust adjustment or small bust adjustment – something that will be determined better after you take more measurements and in the muslin phase.
For your upper bust, waist and hip, you’ll want to take these measurements in your underclothes – whatever that entails – and you’ll want to do it in front of a mirror. This way you can see what’s going on with the tape measure. The upper bust goes around the upper portion of your chest, which may or may not make the tape measure fall perfectly parallel with the floor. Also the measurement doesn’t need to be skin tight, just snug like you could put a finger or two in there with your measurement (note this for all measurements). The waist is taken at the narrowest point of your middle. This may or may not be where you wear things like skirts or pants and even if that is so, you still need a reference point. I put a piece of elastic around my waist and do the hula for a minute while it settles. Then I take my measurement over that. This is crucial for a bodice, but for a skirt or pair of pants, I measure the place on my mid section where I want the waist to hit me and then measure the pattern pieces to see just how much I might need to add or subtract in order to get these types of garments to hit me where I want them to hit me. This involves thinking about ease which I’ll be covering much more in depth later. For the hip, you need to take the measurement right at your hip bone and then again at your widest area below the waist which may or may not be at your hip bone. Let me tell you why. For pants, you need the measurement that is right at your hip bone. The crucial fitting part about pants is that they have to fit those three moving tubes pretty perfectly so you need to take the measurement at this crucial area because those intersections don’t happen mid thigh or what have you. However for skirts and dresses, you’ll want to take your hip measurement at your widest point below your waist. This actually means that you might have a wider measurement just below your hip bone and for skirts, this is much easier to fit. Not impossible to fit, just less work.
I know there are other ways to determine your correct size, but truly after having tried several ways (oh so many ways!!!) I always come back to taking these three measurements this way. They’ve served me well and they’ve also served those that I teach well too. They take care of the bigger headache areas and reduce the amount of work you have to do too. Let me clarify though that these are the things that have worked for me and for others that I have fit and worked with too. But if you feel you are picking the right size and are happy with the way things are working within that size, stay with what you’ve got. Also, you don’t have to take these measurements every time you pick a new pattern. Take them once, write them down, memorize them and then a few years later take them again, just to make sure that nothing has changed or what not. Our bodies will naturally age, things will start shifting and well, you know, that’s how it goes. Just check every few years to see what size bracket you fall into.