Bust vs high bust: which measurement picks your size

Choose a bodice size by your high bust, measured above the bust and under the arms, whenever your full bust is 5 cm (2 in) or more larger than the high bust; then add the missing room with a full bust adjustment. If the difference is under 5 cm, the full bust picks the size, as the chart intends. The reason is that most sewing patterns are drafted for a B cup, a difference of about 5 cm between the two measurements, and the "bust" column of a size chart assumes that proportion.

What is the difference between bust and high bust?

The full bust is the girth around the fullest part of the bust, tape level all the way round, arms relaxed, in the bra you will wear with the garment. It is the number every size chart lists.

The high bust (also called upper bust or upper chest) is the girth above the bust: the tape passes under the arms, high across the back at the shoulder blades and across the chest above the breast tissue. It measures the frame, the ribcage and shoulders, which is what the neckline, shoulder seams and armholes of a bodice actually have to fit.

Take both with the same tape, within a minute of each other, and write down the difference. That difference is your sewing cup, which has nothing to do with your bra size: bra cups are measured against the underbust, sewing cups against the high bust.

Why do size charts assume a B cup?

A bodice pattern is drafted on a block with one set of proportions. Across the sizes the bust grows, and with it the shoulders, the neckline, the armhole depth and the back width, all in fixed ratios. In most pattern lines the ratio corresponds to a B cup: about 5 cm (2 in) more at the full bust than at the high bust.

If your difference is bigger, say 10 cm (4 in), and you pick the size by full bust, you get a bodice whose bust is right but whose shoulders, neckline and armholes are two sizes too big. The neckline gapes, the shoulder seams hang off the shoulder, the armholes are low. Fixing that afterwards means recutting everything above the bust, which is far more work than adding width at the bust. Picking the size for the frame and adding bust room is the other way round: one targeted alteration, and the parts that are hard to alter are already right. How to choose your size covers the same logic for the waist and hip.

How do you use the two measurements, step by step?

1. Measure both. Full bust and high bust, level tape, normal breath.
2. Subtract. Full bust minus high bust.
3. Under 5 cm (2 in): find your full bust in the chart and take that size. No bust adjustment.
4. 5 cm or more: add 5 cm to your high bust and look up that number in the bust column. This is the size whose frame fits you.
5. Work out the adjustment. The room still missing is the difference minus 5 cm. A full bust adjustment on a half-front pattern piece adds half of it; for a 10 cm difference, 10 minus 5 is 5 cm, and the slash in the front piece opens by 2.5 cm (1 in).
6. Check the waist and hip of the chosen size against your own and grade out or in at the side seams where needed; grading between sizes shows how.

The full bust adjustment explained walks through the slash-and-spread with a dart.

What does this look like with real numbers?

In the third row the full-bust method would send you to the 94 cm size, about two sizes up in most charts; the high-bust method keeps you in the 89 cm size and adds 2.5 cm to each front half. Those two garments have the same bust circumference, but one has a neckline and shoulders two sizes too big.

What if the difference is smaller than 5 cm?

Then your frame is larger than the pattern assumes for your bust, and sizing by full bust gives a bodice that is tight across the back and the upper chest while the bust area has slack. Size by high bust plus 5 cm as above; this time the adjustment is a small bust adjustment, closing a wedge in the front rather than opening one. For a 2 cm difference the amount is small, 1.5 cm (5/8 in) per front half, and on a loose garment you can ignore it.

Does the rule apply to every garment?

It applies where a bodice is shaped to the body: fitted and semi-fitted dresses, woven tops with darts, princess seams, anything with a set-in sleeve. The looser the garment, the less it matters.

• Fitted woven bodice: apply it fully. The neckline and armholes are where the fit shows.
• Boxy or oversized top with lots of design ease: size by high bust and skip the adjustment if the difference is under 8 cm (3 in); the ease covers it.
• Knit T-shirt: the stretch takes up to about 8 cm of difference without an adjustment. Beyond that, size by high bust and add width at the bust through the side seams rather than a full dart adjustment.
• Wrap and surplice fronts: size by high bust; the wrap adds room where you need it, and a gaping neckline is the usual complaint when the full bust picks the size.

If you move between European, American and British charts, convert the chosen size with the sewing size converter rather than comparing labels, because the same bust measurement carries three different numbers.

What changes when the pattern is drafted from your measurements?

The size question disappears, because there is no chart to enter. A made-to-measure draft takes the frame and the bust from separate measurements: shoulder width, back and front waist lengths, bust height and the distance between the bust points set the shoulders, neckline and dart position, and the full bust sets the width. Sewly's drafting works that way for women's bodices, so a 15 cm difference between frame and bust is drawn into the pattern at the start, with the dart sized for it, rather than fixed with a slash-and-spread afterwards. What a draft cannot know, how high the bust sits in your preferred bra or how much you like the neckline to stand away, you still check on a toile.