Bust Size to Bra Size
This converter turns a bust measurement into a bra size — with one essential companion number. Enter your bust and your underbust and you get a complete starting size in six systems; enter only the bust and the converter will tell you, honestly, what is missing.
Going from bust size to bra size takes two facts because a bra size is two facts: the band from your ribcage, the cup from the difference between bust and underbust. This page makes both explicit.
Quick answer
To convert bust size to bra size you need two measurements: the bust at its fullest point and the underbust snug under the root. The underbust becomes the band; the difference between bust and underbust becomes the cup. For example, bust 37 in with underbust 32 in converts to US 32DD, EU 70E and JP E70.
6
sizing systems (US, UK, EU, FR/ES, AU/NZ, JP)
460+
charted sizes with bust ranges
2
measurements needed (underbust + bust)
Convert your bust size to bra size
The converter below is the full engine in compact form — inches or centimetres, six systems, sister sizes, all computed in your browser. Enter the bust first, then the underbust; the moment both are present you have a complete bust size to bra size conversion.
Why one number is not enough
A bust measurement alone cannot produce a responsible size, and any tool claiming otherwise is guessing. Consider two people with a 36-inch bust: one has a 34-inch ribcage — a B cup on a 34 band — the other a 30-inch ribcage — a DD cup on a 30 band. Same bust, wildly different bras. The underbust is the missing variable, which is why this converter asks for it before promising anything. Honesty about inputs is what separates bust size to bra size tools from toys.
If you know your bust but have never measured your underbust, the measuring guide takes about a minute to fix that — it is the easier of the two readings.
How the bust size to bra size math works
Step one: band. Inch systems round your underbust to the nearest even number; centimetre systems use a five-step ladder; FR/ES adds 15 to the EU number; AU/NZ uses dress-size bands. Step two: cup. The difference between bust and underbust is snapped to the system's ladder — roughly one letter per inch, with each system's own sequence beyond D.
The result is a starting size — the label the arithmetic supports before brand patterning enters. That is why every conversion here ships with sister sizes: the neighbouring labels most likely to fit when the first one is close but imperfect.
From bust in centimetres to a continental size
If you measure in centimetres, the bust size to bra size path is the same with friendlier arithmetic: an underbust of 81 cm resolves to an EU 70 band, and a bust of 94 cm gives a 13 cm difference — an EU E cup, an FR/ES 85E, a JP E70. One conversion, three continental dialects, no inch arithmetic in sight.
The chart pages make the same trip in table form: the breast size chart maps differences to letters per system, and the bra size chart lists the finished sizes with the bust ranges they fit.
After the conversion: verify the fit
A converted size earns trust the same way a measured one does — on your body. Run the four checks from the fit guide: level snug band, smooth cups, flat gore, quiet straps. If the cups are right but the band is off by a step, swap along the sister sizes the converter shows rather than starting over.
Re-run the bust size to bra size conversion every six to twelve months, after weight changes, or whenever your best bra starts behaving strangely. Two numbers, thirty seconds, no guessing. Two numbers, and the bust size to bra size answer renews itself.
Bust size to bra size: worked examples
Run the bust size to bra size conversion on three bodies and the pattern locks in. A bust of 36 in over an underbust of 34 in — two inches of difference — resolves to 34B. The same bust over a 32 in ribcage gives four inches and a 32D. And a metric example: bust 94 cm over underbust 81 cm is a 13 cm difference — EU 70E, UK 32DD, JP E70. Three answers, one method: bust size to bra size always means bust plus underbust.
Notice what never happens: the bust alone never decides. In every case the second number moves the answer by whole sizes, which is exactly why this page refuses to guess it for you. Run your own pair through the converter above and the bust size to bra size logic becomes yours in one pass. Once you have seen the pattern, every bust size to bra size question — a new brand, a new country, a gift for someone else — reduces to the same two readings and the same subtraction. That is the bust size to bra size method: simple, portable, and honest about needing both numbers.
Frequently asked questions
How do I convert bust size to bra size?
Measure your bust at the fullest point and your underbust snug beneath the root, then enter both into the converter above. The underbust sets the band and the difference sets the cup — that is the complete bust size to bra size conversion. Two numbers in, six labels out — bust size to bra size in thirty seconds.
Can I find my bra size with only my bust measurement?
No. The same bust sits on many ribcages, so the cup — the difference — cannot be known without the underbust. The converter asks for both rather than guessing.
What bra size is a 36 inch bust?
It depends on the underbust: with 34 in you get roughly a 34B; with 32 in, a 32D. That dependence is exactly why bust size to bra size needs two numbers. The bust size to bra size lesson is that dependence itself.
Does the converter work in centimetres?
Yes — switch the unit toggle to cm. EU, FR/ES and JP labels are naturally centimetre-based, so continental results read directly from your metric measurements. Centimetres make the bust size to bra size path even smoother.
Why did my converted size differ from my old label?
Either your measurements moved, your old label was never measured, or the brand's patterning runs away from the chart arithmetic. Keep the measurements as ground truth and fit-test the result. Trust measurements over memory in every bust size to bra size conversion.
What are sister sizes in this conversion?
Neighbouring labels with similar cup volume — one band down with one cup up, or the reverse — shown per system with every result. They are the quickest fix when a converted size is nearly right.
What bra size is a 94 cm bust?
It depends on the underbust: 94 cm over 81 cm is about EU 70E / UK 32DD, while 94 cm over 86 cm is closer to 75C. Bust size to bra size conversion always needs both numbers — try the converter above with your own pair. Bust size to bra size arithmetic never changes; only the inputs do.
How do I convert bust size to bra size for a gift?
Ask for — or discreetly borrow — both readings, because bust size to bra size conversion always needs the underbust too. With the pair in hand, the converter above prints the six-system labels in seconds. Gifting works because bust size to bra size needs facts, not guesses.
Can I do a bust size to bra size conversion from an old bra label?
Only if you trust the label. The honest bust size to bra size path runs through fresh measurements, so a two-minute tape session beats any label-based bust size to bra size shortcut. Fresh tape readings keep bust size to bra size conversions honest.
Is bust size to bra size conversion different for sports bras?
The bust size to bra size method stays the same; consult the brand chart for where its labels land, and keep both readings as your reference. The bust size to bra size method is category-proof.
Sources & standards
Every size on this site is cross-checked against these published standards and chart families before it ships.
- 2017
ISO 8559-1:2017 — Size designation of clothes — Part 1: Anthropometric definitions for body measurement
Defines the body measurement points (chest/bust girth, underbust girth) this site measures.
- 2017
EN 13402 (label family) — Size designation of clothes — European size labelling
Basis of the continental EU band ladder (65, 70, 75 …) in 5 cm steps.
- 2023
JIS L 4006:2023 — Sizing systems for foundation garments
Japanese foundation-garment sizing; the label family behind JP cup-first sizes such as C75.
- 2019
KS K 9404 — Sizing systems for foundation garments (Korea)
Korean foundation-garment sizing; referenced while the KR system awaits full verification.
- 2025
Multi-source retail consensus — US, UK, FR/ES and AU/NZ bra size charts (cross-brand average)
Inch-based band rounding, UK double-letter cup ladder, FR/ES +15 offset and AU/NZ dress-size bands.
By Bra Size Calculator ·