Calculator + visual reference
Your size, plus the chart that explains it
Most calculators just hand you a letter. This one shows the full picture — enter two measurements to get your size, then see exactly where it sits on the complete band-and-cup chart below.
Snug and level, directly under the bust, over a thin or no bra.
Loose and level across the fullest point, without pressing in.
Enter both measurements to see your result.
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Approximate shape reference — real cut varies by brand.
The full reference
The complete band-and-cup chart
Rather than a single answer, here is every combination at once. Find your band across the top and your bust-to-band gap down the side — the cell where they meet is your size. Calculate above to highlight your own cell.
Rows are labelled by bust-minus-band difference in inches; the resulting cup letter follows the standard AA–H progression used across most English-speaking markets.
Reading the letters
Cup letter isn't cup volume
A D cup on a 30 band holds noticeably less than a D cup on a 40 band, even though the label reads identically. This scale gives a rough sense of how relative volume builds as the letters climb, independent of any one band size.
The method
Where the numbers in the chart come from
Every cell above is built from the same simple rule fitters use today, not the older habit of padding a few inches onto your underbust for stiffer, less forgiving fabric.
Underbust reading
A snug, level tape directly beneath the bust. Round to the nearest whole number — that becomes the band column you'll look up.
Bust reading
A loose, level tape across the fullest point, resting rather than compressing.
Cross-reference
Subtract band from bust to get your row on the chart. That row's letter, next to your band's column, is your size.
cup difference = round(bust, in) − band
0=AA · 1=A · 2=B · 3=C · 4=D · 5=DD/E · 6=F · 7=FF · 8=G
Worked example
An underbust of 86 cm (≈33.9″) rounds to a band of 34. A bust of 104 cm (≈40.9″) rounds to 41, a 7-inch gap that lands on FF — giving 34FF. If that's hard to find in stock, the sister sizes 36F or 32G hold nearly the same volume.
Before you shop
Reading errors that skew the chart
Padded bra on the bust reading
Foam and moulding push the bust number up artificially. Take that measurement in a thin, unlined bra or nothing at all.
Band pulled too tight
The band figure should feel secure, not compressed — two fingers should slide comfortably underneath.
Tape sitting unevenly
A quick mirror check confirms the tape hasn't crept upward at the back while you read the front.
Reading one brand's tag as universal
Every chart cell describes a formula, not a specific brand's cut — treat your result as a lookup starting point.
Ignoring the diagonal sister size
If your exact cell is out of stock, the size diagonally adjacent on the chart usually fits almost identically.
Assuming the chart cell is permanent
Weight change, pregnancy, nursing or a new fitness routine can shift which cell actually fits within months.
Questions
Frequently asked questions
These are our 15 most-asked. The complete FAQ page covers 25, and you can search it.
Each cell comes from the same rule: band equals your rounded underbust, and cup letter equals how many inches your bust exceeds that band. The chart is that rule laid out visually instead of calculated one entry at a time.
Not exactly. The letter tracks a difference in inches, but actual volume shifts with band size too — a 30D and a 40D hold noticeably different amounts despite sharing a letter.
The letter only captures an inch difference, not shape, root width, or how a brand cuts its pattern — two "C cups" from different labels can sit quite differently.
A size sitting diagonally from yours on the chart — one band up and one cup down, or the reverse — carrying roughly the same volume.
Every 6 to 12 months, and always after a significant weight change, pregnancy, breastfeeding or surgery.
That padding trick compensated for stiffer, older fabric. Modern elastic doesn't need the buffer, so today's chart works straight from your real underbust number.
Every brand builds its own cutting block, so identical chart coordinates can fit slightly differently depending on the label — completely normal, and exactly why sister sizes exist.
Usually not for long — a loose band rides up and shifts support onto the straps. A band that sits level and snug on the loosest hook is the one that actually holds up through a day.
The size labels are shared, but wire-free and soft-cup styles often run a little roomier, so some people move down a cup letter in those styles.
Yes — the chart only encodes circumference and a volume difference, not shape. Root width and projection still vary widely within one cell.
Cup volume, the row, tends to respond first to weight change, pregnancy or nursing, while the band column stays comparatively steadier.
Level band staying on the loosest hook, a centre gore flat against the breastbone, and cups holding everything smoothly with no spilling or gapping.
There's no single global standard above a D cup, so brands label that row differently — DD, DDD or E can all describe the same chart position depending on the brand.
Try the sister sizes shown with your result — same volume, different band, and typically easier to actually find in stock.