34B Bra Size
34B measurement ranges
34 = the band, built around an underbust of about 86 cm (34 in).
- Underbust range
- 33.5–34.5 in
- Bust range
- 35.5–36.5 in
- Bust − underbust difference
- 1.5–2.5 in
34B in other sizing systems
B = the cup, a bust−underbust difference of roughly 1.5–2.5 in.
US
34B
UK
34B
EU
75B
FR/ES
90B
AU/NZ
12B
JP
B75
34B sister sizes by system
US · 34B
tighter: 32C · looser: 36A
UK · 34B
tighter: 32C · looser: 36A
EU · 75B
tighter: 70C · looser: 80A
FR/ES · 90B
tighter: 85C · looser: 95A
AU/NZ · 12B
tighter: 10C · looser: 14A
JP · B75
tighter: C70 · looser: A80
Ranges come from common sizing conventions; individual brands may cut their own patterns.
A 34B bra size pairs a 34 band with a B cup: the band is built around an underbust of roughly 34 inches (about 86 cm), and the B cup adds a difference of about two inches between bust and underbust. Decode it once and every other label decodes the same way.
Below you will find the full anatomy of the 34B bra size — the measurement ranges it is designed for, its equivalents in six international systems, its sister sizes in each of them, and how to check whether 34B is actually your size.
Quick answer
A 34B bra size means a 34 band — snug underbust near 34 in (86 cm) — with a B cup, so a bust near 36 in (91 cm). The same size is written EU 75B, FR/ES 90B, AU/NZ 12B and JP B75. Its sister sizes are 32C and 36A in US/UK sizing.
6
sizing systems (US, UK, EU, FR/ES, AU/NZ, JP)
460+
charted sizes with bust ranges
2
measurements needed (underbust + bust)
The 34B bra size in numbers
The panel below unpacks the 34B bra size from the sizing engine's own data. The band half: an underbust range around 86 cm where a 34 band is designed to sit. The cup half: a difference of roughly 1.5–2.5 in (4–6 cm) between bust and underbust, which is what the B encodes. Together they put the bust range for a 34B bra size near 90–93 cm — about 35.5–36.5 inches.
These ranges are the chart arithmetic speaking, not a promise about your body. Brands cut patterns around their own blocks, so a 34B bra size from one label can fit like its neighbour from another — the fit checklist settles it.
What the 34 and the B each mean
The 34 is the band — the number, in inches, around the ribcage. It carries most of the bra's support and should sit level and snug, fastened on the middle hook when new. The B is the cup — the letter for a bust that exceeds the underbust by about two inches. Neither part stands alone; a 34B bra size is exactly the pair.
Change one part and you change the meaning: on a 36 band the same two-inch difference is a 36A; on a 32 band it is a 32C. That is the sister-size mechanic living inside this one label. The 34B bra size is the cleanest worked example of that mechanic.
34B in six international systems
The same body that wears a 34B bra size wears UK 34B, EU 75B, FR/ES 90B, AU/NZ 12B and JP B75. The band arithmetic differs — inches rounded to even, centimetres stepped by five, dress sizes, and Japan's cup-first notation — but the measurements behind the label are identical.
Beyond B the alphabets fork (UK DD versus continental E), but at B every system agrees, which makes the 34B bra size a clean worked example for cross-border shopping. The bra size chart generalises the view to every band and cup.
Sister sizes of the 34B bra size
In US/UK sizing the sisters of the 34B bra size are 32C — same volume, tighter band — and 36A — same volume, looser band. In EU labels, 75B trades to 70C and 80A; in Japan, B75 trades to C70 and A80. Reach for the tighter sister when the band of your 34B rides up but the cups still fit; the looser one when the band digs.
Because band stretch varies by brand, sister sizes are also the standard workaround when a 34B bra size from one label feels tighter than another: same cup volume, one band step, comfort restored.
Is 34B your size?
Measure rather than assume: a snug underbust near 86 cm and a bust near 91 cm points to the 34B bra size. Run both readings through the calculator for the full six-system verdict, then confirm on the body with the four fit checks — level band, flat gore, smooth cups, quiet straps.
If the cups of your 34B gape, tighten the straps and check the band before dropping to an A; if they spill, first check that the band is not riding up and inflating the apparent cup. The B cup page covers this letter's typical fit profile in depth. Fit checks finish what the 34B bra size arithmetic starts.
34B bra size: quick reference
The 34B bra size in one line each. The band: 34, fitting an underbust near 86 cm or 34 inches. The cup: B, a two-inch difference, putting the bust near 91 cm or 36 inches. The equivalents: UK 34B, EU 75B, FR/ES 90B, AU/NZ 12B, JP B75. The sisters: 32C and 36A in inch systems, 70C and 80A in continental ones. The checks: level band, flat gore, smooth cups, quiet straps.
That is the entire 34B bra size decoded — two measurements, six dialects, two sisters. Run your own numbers through the calculator and see whether the 34B bra size is your label or just a neighbour of it. Either way, the 34B bra size now reads like plain English.
Frequently asked questions
What is a 34B bra size?
A 34 band with a B cup: the band fits an underbust near 34 in (86 cm) and the cup fits a bust about two inches larger, near 36 in (91 cm).
What measurements make a 34B?
An underbust of roughly 85–89 cm (33–35 in) and a bust of roughly 90–93 cm (35.5–36.5 in). The panel above shows the exact ranges the engine uses. Two readings decide any 34B bra size claim.
What is 34B in EU or UK sizing?
UK uses the same label, 34B. A 34B bra size is EU 75B, FR/ES 90B, AU/NZ 12B and JP B75 — all describing the same measurements. Every 34B bra size label points at one body.
What are the sister sizes of 34B?
32C and 36A in US/UK sizing; EU 75B trades to 70C and 80A. Sister sizes keep cup volume nearly constant while the band changes. Sister trades are how a 34B bra size stays wearable across brands.
Is 34B average?
It sits near the middle of common fitted sizes, though fitted reality skews larger in the cup than most people assume. Only your measurements can say whether it is your size. Only fresh measurements crown a 34B bra size.
34B vs 34C — which do I need?
One inch of difference: the C cup fits a bust near 37 in on a 34 band. If your 34B cups spill, try 34C; if they gape after strap and band checks, stay with B or try a shallower style. Checks first, letter second — that protects the 34B bra size verdict.
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.
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