Core Size (Symmetric) Grading
Core sizes are typically defined as those falling between 30 – 38, A – D, sometimes including DD. The grade rules that are applied to the cup are symmetrical. The increments we apply on the left of the cup are equal to those applied to the right of the cup. The image below has been drafted and graded in Adobe Illustrator.
What is grading?
Grading is the formulae for creating different sizes based on a single base or core size, originally invented in Germany in the early 1900s by clothing production engineers. (FAUST, M-E., and CARRIER, S. (eds.), 2014)
Bra grading is complex and varies from brand to brand. It is not something that brands discuss or share openly, as it can be seen as proprietary information, but if you have a couple of bras from the same range in relatively similar sizes, you can measure the bras and try to ‘crack’ the measurements they use.
In the diagram below, traditionally we grade the depth of the bra cup by 12.5mm and the width of the cup by 12.5mm. The distribution of the proportion will depend on the size of the bra.
Plus Size (Asymmetric) Grading
Plus sizes are typically defined as those falling beyond the D/DD cups and all band sizes. Plus size cup grading is considerably different from Core Size grading as the grade is applied asymmetrically to the cup. More cup volume is added to the cup nearer the underarm, rather than near the centre front, in order to keep the point of bust centred and forward facing. In the pattern pieces below, you can see that the growth of the cup radiates outwards from the point of bust (nipple area of cup). The image below has been developed and graded in Lectra Modaris software.
Plus Size Wire Grade
Plus size underwires grow by a smaller amount, and 16mm is commonly seen in UK lingerie brands. The overall growth is smaller as there are typically more sizes in a range, where a 21mm grade would have an oversized wire when getting to very large cup or band sizes.
Band Size Grading
Another method of grading to consider is the grade applied to the band size. Outerwear garments are typically graded by 2” or 50mm, as are the bands of many bra companies.
A 40mm system, typically attributed to the French, is also seen in band grades. This method of grading will affect the fit of a bra, and the wearer may find certain brands feeling tighter or looser than others.
The grading system used by manufacturers is not typically transparent, and becomes a part of their ‘trade secrets’ but information can be deduced when measuring bras for comparison.
I was able to measure a few brands and conclude the following:
40mm system (French)
50mm system (others)
- Curvy Kate
Industry standard sample size is traditionally a 34B. There are standard measures used when drafting patterns for band size and bust projection and depth. A 34 band is typically 64cm in length with the cradle of the bra 32cm and each wing of the bra 16cm.
Core Size Wire Grade
A 21mm wire grade is common. There is a line of wires available in a variety of styles developed for Marks & Spencer that are widely available for independent brands and hobbyists to use. The ‘MS’ wires are predominantly available in core sizes and grow in length by 21mm for each size.
Underwires also have a grade rule applied to them. Each increase in wire size will grow by a measurement anywhere from 14 to 21mm.
As you can see by the charts above, there will be subtle fit differences in the underbands at the ends of the size range depending on the method used. It would explain why some wearers find some bands looser or firmer than other brands in the same size, as well as why some people may find the same brand to be firmer than usual or looser than usual depending which side of the base size you are on.
For example: when comparing a bra using a 40mm system, perhaps a Freya bra, against a bra using a 50mm system, perhaps a Cleo bra, someone wearing a 28” band may find that the Freya bra fits looser than the Cleo, and someone in a 38” band may find the opposite, and that the Freya is tighter. This would be due to the 40mm system being used and comparing the fit to a bra using the 50mm system.
Grading can be laboriously done by hand, or on the computer. Adobe Illustrator can be used for basic grading shifting points along a X-Y axis, although more specialized pattern software such as Lectra or Gerber are used for pattern development and grading in the apparel industry.
FAUST, M-E., and CARRIER, S. (eds.) (2014) Designing apparel for consumers. Cambridge: Woodhead Publishing Limited
Educating women on the benefits of proper fitting bras is important to Kim. Designing lingerie that complements the fuller figure, and is comfortable, on-trend and beautifully constructed is her mission.
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