How to Measure Your Bra Size at Home: A UK Sizing Guide

Professional bra fitters have said it for years: most women are wearing the wrong size, and it usually takes less than five minutes with a tape measure to find out. An ill-fitting bra isn't just uncomfortable — a band that's too loose stops giving support the moment you move, and cups that are too small create the "quad-boob" look that no amount of adjusting fixes. The good news is that you don't need a fitting appointment to get an accurate size. Here's exactly how to measure yourself at home, how to read the result in UK sizing, and the fit mistakes worth checking for even if you think you already know your size.

What You'll Need

Grab a soft fabric tape measure — the kind used for sewing, not a rigid DIY tape — and put on a bra that fits reasonably well and isn't padded, or take your measurements without one. Stand in front of a mirror if you can, and have a pen and paper ready to jot the numbers down, since you'll be using them together in a moment.

How to Measure Your Band Size

Wrap the tape measure directly under your bust, around your ribcage, keeping it horizontal all the way round — it should sit snug against the skin without digging in or slipping down at the back. Breathe out normally and take the reading in inches. Round to the nearest whole number, and if you land on an odd number, round up to the next even number. That figure is your band size. This direct-measurement method is what most UK retailers and fitting services use today; you may still see older guidance that adds four or five inches to the underbust measurement, but that method predates modern stretch fabrics and tends to overestimate the band, so it's best avoided.

How to Measure Your Bust (Cup) Size

Next, wrap the tape measure around the fullest part of your bust — usually across the nipple line — keeping it level front to back and not pulled tight enough to compress anything. Round this measurement to the nearest whole inch as well. This is your bust measurement, and the difference between it and your band measurement is what determines your cup size.

How to Calculate Your UK Cup Size

Subtract your band measurement from your bust measurement. Each inch of difference corresponds to one UK cup letter:

  • 0 inches — AA
  • 1 inch — A
  • 2 inches — B
  • 3 inches — C
  • 4 inches — D
  • 5 inches — DD (E)
  • 6 inches — E (DDD)
  • 7 inches — F
  • 8 inches — FF
  • 9 inches — G

So a 34-inch band with a 38-inch bust measurement (a 4-inch difference) gives a UK size of 34D. Write your band number followed directly by your cup letter, and that's the size to start trying on.

Reading UK Bra Sizing and Sister Sizes

UK cup lettering runs AA, A, B, C, D, DD, E, F, FF, G, GG, H and upward — note that UK sizing differs from US sizing once you pass a D cup, since a UK DD is roughly equivalent to a US E. If your exact calculated size isn't in stock, it helps to know about sister sizing: moving one band size down and one cup size up (or the reverse) gives a very similar cup volume. A 34D, for example, sits close to a 32DD or a 36C in actual cup volume, even though the numbers look quite different. This is useful for trying a neighbouring size when a particular style runs slightly big or small.

Common Bra Fit Mistakes to Avoid

  • Band too loose. The band should feel snug on the loosest of its three hooks when the bra is new, since it will stretch slightly with wear — start on the loosest hook and you'll have nowhere to go once it does. Around 80% of a bra's support should come from the band, not the straps.
  • Band riding up at the back. If the band rides up rather than sitting horizontally all the way round, it's too big — try sizing down the band and up a cup to compensate.
  • Cups too small. Spilling over the top or sides of the cup (sometimes called quad-boob) means you need a bigger cup, not necessarily a bigger band.
  • Cups too large. Gaping or wrinkled fabric at the cup means it's too big — size down a cup and check the band still fits.
  • Straps doing all the work. If your straps are constantly slipping or digging in, the band underneath probably isn't providing enough support on its own.
  • Assuming one size fits every style. Cut varies between brands and even between styles from the same brand, so it's worth checking fit each time rather than buying on size alone.

Wireless vs Underwired: Which Is Right for You?

Underwired bras give more structure, lift and definition, and tend to suit fuller busts best since the wire distributes weight along the ribcage rather than relying on fabric alone. Wireless and soft-cup styles trade a little of that shaping for comfort — they're a good choice for everyday wear, sleep, sensitive skin, or smaller cup sizes that don't need as much support to stay in place. Neither is inherently "better"; a well-fitted wireless bra, like our seamless wirefree support bra, can be just as supportive day to day as an underwired style, provided the band fits properly. If you move between the two, keep both sizes on hand, since wireless styles often run slightly differently to underwired ones even within the same size.

When to Re-Measure

Your size isn't fixed for life. Weight changes, pregnancy and breastfeeding, and simply the natural wear of an older bra can all shift your measurements, so it's worth re-measuring roughly once a year, or any time a well-fitted bra suddenly starts riding up, gaping, or digging in. The five-minute method above works exactly the same the second time round.

Shop Your New Size

Once you know your size, browse our Bras & Sports Bras collection to find your fit. If you'd rather not think about coordinating a bra separately, many of our lace bodysuits and babydoll sets come with built-in cups, so getting your size right here pays off there too — our guide on five ways to style a lace bodysuit is a good place to start.

Laven & Ivory is a UK-based lingerie and nightwear brand offering elegant, affordable pieces in UK sizes, shipped from our Lancashire warehouse with free UK delivery and easy returns.

Back to blog