The Bra Sizing Problem
Studies and anecdotal evidence from lingerie fitters consistently suggest that a large proportion of women are wearing the wrong bra size — typically too large in the band and too small in the cup. This happens for several reasons: outdated measuring methods, limited size availability in high-street stores, and the fact that most of us were fitted as teenagers and never revisited it.
The good news is that measuring yourself at home is straightforward, and getting closer to your correct size can transform your comfort and how your clothes fit.
What You'll Need
- A soft fabric measuring tape
- A well-fitting (non-padded) bra or no bra
- A mirror, or a friend to help
Step 1: Measure Your Band Size
Wrap the measuring tape snugly around your ribcage, directly beneath your bust. The tape should be level and firm — not tight enough to dig in, but not so loose that you could fit a fist underneath it.
Take note of this measurement in inches. If it's an even number, that's your band size. If it's an odd number, round to the nearest even number (so 31 inches becomes 32, and 33 inches becomes 34).
Important: Do not add 4–5 inches to this measurement, as older guides sometimes suggest. That method was designed for older bra constructions with little stretch. Modern bra bands are stretchy enough that you should use your actual measurement.
Step 2: Measure Your Bust
Measure around the fullest part of your bust — typically across the nipples. Keep the tape parallel to the floor and don't pull too tight. Take this measurement while wearing a non-padded bra for the most accurate result.
Step 3: Calculate Your Cup Size
Subtract your band measurement (Step 1) from your bust measurement (Step 2). The difference determines your cup size:
| Difference (inches) | Cup Size |
|---|---|
| 1 inch | A |
| 2 inches | B |
| 3 inches | C |
| 4 inches | D |
| 5 inches | DD / E |
| 6 inches | DDD / F |
| 7 inches | G |
| 8 inches | H |
Understanding Sister Sizes
One of the most useful concepts in bra fitting is sister sizing. Cup volume is relative to band size, meaning the same cup volume comes in different combinations of band and cup letters. For example, a 34DD and a 36D and a 32F all contain the same cup volume — just on different band sizes.
This is useful when:
- A style doesn't come in your exact size
- You're between sizes and want to find the best fit
- You're shopping internationally with different size charts
To go up a sister size: increase the band by 2 and go down one cup letter (e.g., 34DD → 36D). To go down: decrease the band by 2 and go up one cup letter (e.g., 34DD → 32F).
Signs Your Current Bra Doesn't Fit
- The band rides up at the back — band is too large
- Straps digging in or falling off — band is likely too large (straps are compensating)
- Cup spillage at the top or sides — cup is too small
- Gaping cup — cup is too large, or the style doesn't suit your breast shape
- Underwire sitting on breast tissue — cup is too small
- Centre gore not lying flat — cup is too small, or the style isn't right for your shape
A Word of Caution on Online Calculators
Bra size calculators online vary significantly in the method they use, and many still apply the outdated "+4 inches" rule. Use your measurements as a starting point, but be prepared to try adjacent sizes. The only true test of whether a bra fits is putting it on.
When to Get Re-Measured
Your size can change due to weight fluctuation, hormonal changes, pregnancy, breastfeeding, and natural ageing. It's worth re-measuring every year or so, or whenever your current bras start feeling less comfortable than they used to.