Bra Fit Lab / Fit Science

How to measure your bra size at home — the evidence-based way.

Two measurements, one minute. We show the method, the chart, and the sources — body-neutral, no hype, no sales pitch.

2 MEASUREMENTS~1 MINNO PADDED BRA

Read the full method →

FIG.1 — Tape placement

Measure Sister sizing Fit checks Size chart FAQ

85%

wore the wrong fit*

80 / 20

band vs. strap support

6–12 mo

re-measure interval

*2010 study cited by Healthline. Figures sourced inline; see the guide.

FLAGSHIP METHOD

The complete at-home measuring method

Band, bust, and cup in three steps — with a printable chart, in-mirror fit checks, and every figure sourced to NHS Frimley Health, Healthline and Cleveland Clinic.

Open the method →

How the Lab works

01

We start with the tape

Every guide leads with the measurement or the test — numbers first, opinions second.

02

We show our sources

Claims are cited inline to clinical and research sources, and uncertainty is flagged out loud.

03

We stay body-neutral

The garment should fit the body — never the other way around. No shame, no miracle claims.

Reference card

Sister sizing at a glance

Same cup volume, different band. If the band feels loose but the cup fits, go down a band and up a cup (and vice-versa). Mono columns below read like a spec sheet.

If you wear	Band too loose →	Band too tight →
34C	32D	36B
36B	34C	38A
32D	30DD	34C

Cup letters are not standardised across brands — treat this as a map, not a law.

"Most people are guessing, and a tape measure beats a guess. The band does about 80% of the work — if you're cranking your straps to feel held up, your band is too loose, not the other way around."

— Bra Fit Lab, Fit Desk

Fit questions, answered

How do I measure my bra size without a tape measure?+

Use a length of string or a phone-charging cable, wrap it exactly where the tape would go, mark where it overlaps, then hold it against a ruler. The method is identical — you're just borrowing a straight edge.

Should I round my band size up or down?+

Measure snug and round to the nearest inch first. If you're between bands, try the smaller (tighter) band too, since bands loosen with wear and washing. Always test on the loosest hook so you have room to tighten later.

Why does my size feel different between brands?+

Because band and cup labels aren't standardised — a 34C in one label can fit like a 34D in another, and international sizing differs again. Use your measurements as a baseline and the in-mirror fit checks as the real test.

How often should I re-measure?+

Every 6 to 12 months, and any time your weight changes, you're pregnant or postpartum, or your bras suddenly stop fitting. Your body isn't static, so your size won't be either.

Can a bra reshape or shrink my breasts?+

No. Bras support and shape your silhouette while worn; they don't permanently reshape breast tissue or cause fat loss. For medical concerns, consult a healthcare professional.

Fall between sizes, or want more structure under a fitted top?

Shaping and support styles can bridge the gap once you know your numbers.

Browse Shapeshe's bras

DO

Fit Desk · Reviewed for accuracy · Updated Jun 2026

Dana Okafor

Bra Fit Lab's editorial fit desk — background in apparel and pattern design. We publish fit guidance, not medical advice; figures are cited inline and uncertain ones are flagged. For breast pain or other concerns, talk to a healthcare professional.

Some outbound links may be sponsored. Our editorial stance is no paid placement — sources and methods are chosen on merit.

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