Anatomy of a size label
A label such as 34C or 75C encodes two decisions. The number is the band: an even inch-based number in US and UK charts, a 5 cm step number in European charts. The letter is the cup, and it is relative: C means a bust roughly three inches fuller than the underbust on a US chart, and it means the same letter only within that chart's own sequence. A 30C and a 38C share a letter but not a volume, because the letter is measured from a different baseline.
This relativity is the single most misunderstood point in consumer sizing, and it is the reason charts look confusing. The letter answers the question: how much fuller is the bust than the ribcage underneath it. Change the ribcage, and the same tissue answers with a different letter.
What a chart coordinate actually represents
Read a chart as a map. The columns are band labels, usually 28 to 44 in even steps in US and UK charts, or 65 to 100 in 5 cm steps in European charts. The rows are cup letters. A cell is one SKU the plant can cut, sew and stock. Three properties of the map matter to a buyer:
- Cells on one row share a letter but not a volume; volume grows with the band.
- Cells on one diagonal share an approximate volume; these are the sister sizes.
- The map edges are construction limits, not body limits: a plant stops where its wire range, molding forms or grading skill stop, which is why published ranges differ by line.
The construction limits are visible on this site: the lines on the bras category page publish different band and cup windows for balconette, strapless, wireless and sports constructions, because each construction is graded from its own base pattern.
Sister sizes: moving along the diagonal
Go up one band and down one letter, or down one band and up one letter, and the cup volume stays roughly constant while the band circumference changes. These are sister sizes, and they are the practical tool for the most common fit complaint: the band is right but the cup is not, or the other way round.
| Band label | 30 | 32 | 34 | 36 | 38 |
|---|---|---|---|---|---|
| Letter for the same volume | DD | D | C | B | A |
A consumer fitted at 34C whose band rides up moves to a 32D; one whose band digs moves to a 36B. The tissue volume is unchanged, but the wire angle, the side depth and the band tension all move with the band, which is why the fit changes even though the volume does not. UK charts write the 30 cell as E rather than DD; the volume logic is identical.
For a brand, the diagonal is a planning tool as much as a fit tool. Defining which diagonal families a range covers keeps the SKU count sane: a grid built from two or three volume families across four bands is a manageable first program, while a full rectangle of six bands and six cups multiplies the same fabric and trim across thirty-six size SKUs. The cup volume note develops this with production examples.
Where regional charts stop matching
Up to a D cup, the US, UK and European letter sequences agree well enough for most published conversion tables. Above a D they diverge, because the US sequence doubles letters while the UK and European sequences continue with new single letters or doubled-letter pairs of their own.
| Difference (in) | US | UK | EU | FR |
|---|---|---|---|---|
| 4 | D | D | D | D |
| 5 | DD | DD | E | E |
| 6 | DDD or F | E | F | F |
| 7 | G | F | G | G |
| 8 | H | FF | H | H |
The safe reading is positional, not literal: count steps from D rather than matching letters. A UK F is two steps above a UK D, and so is a US G, which is why the two rows correspond even though the letters do not. The full band and letter conversion tables are in the conversion guide.
Publishers disagree even within one region, which explains why two consumer charts can hand the same measurements two different starting sizes. One chart rounds the underbust up to the next even number, another to the nearest; one counts the cup from the exhale measurement, another from a looser reading. None of these choices is wrong, but each one moves the cell by a step. When a brand inherits a chart from a supplier or a marketplace template, the desk re-derives it as measurements first, so the program knows which convention it has actually committed to before grading starts.
Using charts in a buying context
Charts drawn for consumers assume the reader will accept a starting size and adjust by fit. A brand cannot hand that assumption to a plant. The desk's practice is to fix an internal master grid first - the band run, the cup run and the sister-size families, written as measurements and tolerances rather than as letters - and then overlay per-market label equivalents for the markets the program ships to. Consumer-facing charts are generated from the master grid, not copied from another brand's chart, because a copied chart imports someone else's grading base and fit expectations.
When a program is scoped, the chart closes into paperwork: the master grid goes into the spec sheet, plants confirm which cells they can serve from tooling and which need new grading, and minimums per color follow the size ratio. The desk confirms all of it in writing per program; reference figures are on MOQ and lead time and the size run can be submitted through the quote form. The measurement method behind the grid is in how to measure bra size.