To measure your bra size at home, take two numbers with a soft tape: your band (snug around your ribcage, just under the bust) and your bust (around the fullest point). The band, rounded to the nearest even number, is your band size. The difference between bust and band gives your cup: one inch is roughly an A, two an B, three a C, four a D, five a DD/E, and so on. You need a soft measuring tape, a non-padded bra or none at all, and a mirror. That is the whole method.
What you need before you start
A flexible cloth or sewing tape, not a metal one. Wear a thin, non-padded bra or measure bare — a padded cup adds inches and skews the cup result. Stand upright in front of a mirror so you can keep the tape level all the way around. Measure in inches if you want results that match most US and UK size charts.
The three steps
Two measurements, one subtraction. Keep the tape parallel to the floor for both.
| Step | What to measure | How to do it |
|---|---|---|
| 1. Band | Around your ribcage, directly under your bust | Pull the tape snug and level. Exhale. Round to the nearest whole number — if it lands on an odd number, round up to the next even one. This is your band size. |
| 2. Bust | Around the fullest part of your bust, usually across the nipple line | Keep the tape loose enough to stay level, not pulling the tissue flat. Round to the nearest whole number. |
| 3. Cup | Bust minus band | Subtract your band number from your bust number. The difference in inches tells you the cup letter — see the chart below. |
Cup conversion chart
Once you have both numbers, subtract band from bust and read across. The difference is what sets the cup — the band number stays the same.
| Bust minus band | US cup | UK cup |
|---|---|---|
| 1 in | A | A |
| 2 in | B | B |
| 3 in | C | C |
| 4 in | D | D |
| 5 in | DD / E | DD |
| 6 in | DDD / F | E |
| 7 in | G | F |
So a 33-inch band rounds to 34, and a 38-inch bust gives a four-inch difference — a 34D. If you sit between sizes, the band and cup work as a pair: go down a band and up a cup for a closer fit, or up a band and down a cup. This is called sister sizing, and it is why two labels that look different can fit almost the same.
The mistakes that throw your size off
Most home measurements go wrong in the same few places, and the fix is simple each time. A tape that drifts up your back makes the band read too large. A padded bra during the bust step adds a cup you do not have. Pulling the tape tight on the bust step flattens the tissue and shrinks the cup. And measuring once and trusting it — your size shifts with cycle, weight, and time of day, so two readings on different days are worth the minute.
The band does most of the work. It should sit level and firm enough that two fingers slide under it but no more. If your straps are digging in or the band rides up, the band is usually too big, not the straps too tight. Our guide to why your bra doesn't fit walks through the signs in order, and if you wear a soft-wire or wireless style, whether smaller busts need underwire covers how shape changes what to look for.
What your numbers point you toward
With a band and a cup in hand, you can shop by fit rather than guesswork. For A-to-C cups, a soft floral set like the Margot Lace Set or the smoothing support of the Sabine Lace Set sits well day to day. If you measure into the D-to-E range, the Delphine Lace Set is cut to be fuller-bust friendly without flattening the lace. Browse the everyday collection for pieces you can wear under anything, or the fuller-bust collection if your cup runs D and up. Every cup is lined inside so the lace sits soft against your skin and never itches, sizing runs through D-E on many styles, and your first size exchange is free within 30 days — so a slightly-off measurement is easy to correct. Pieces ship from a US warehouse with tracking and arrive in plain, discreet packaging. Start with your measured size, see how the band sits, and adjust from there with confidence.
Frequently asked questions
What if my band measurement is an odd number?
Round it up to the nearest even number. Bra bands come in even sizes — 32, 34, 36 — so a measurement of 33 becomes a 34 band. If you find the band feels loose once you try the bra on, the elastic may have given a little; in that case the next size down on the band, paired with the next cup up, often fits closer. Trying both readings on different days helps you land between rounding up and down with more confidence.
Can I measure my bra size without a tape measure?
You can get close with a piece of string and a ruler. Wrap the string snug under your bust, mark where it meets, then lay it flat against a ruler to read the band. Repeat across the fullest point for the bust. It is less precise than a soft tape, so treat the result as a starting size rather than a final one. Since a first size exchange is free within 30 days, you can order your best estimate and adjust once you try it on.
Why does my measured size feel wrong when I try it on?
Numbers give you a starting point, not a guarantee, because cup shape, wire width, and lace stretch differ between styles. A measured 34C can feel snug in one cut and roomy in another. Check the band first: it should be level and firm, with the wires or seams sitting flat against your ribcage, not on breast tissue. If the band is right and the cup gaps or spills, adjust the cup up or down a letter. Sister sizing lets you keep the same fit feel while shifting the band.
How often should I re-measure?
Every six to twelve months, or any time your weight, cycle, or comfort changes noticeably. Bodies shift, and so does elastic — a band that fit a year ago may have loosened with washing and wear. Re-measuring takes a minute and saves you from quietly wearing the wrong size for months. If your current bras have started riding up at the back or the straps slip, that is usually your cue to take fresh numbers.
What is the difference between US and UK cup sizes?
The band numbers match, but the cup letters diverge above a D. US sizing uses DD, DDD, then G; UK sizing uses DD, E, F. So a US DDD is roughly a UK E. When you shop across labels, go by the inch difference between your bust and band rather than the letter alone — that number is consistent, while the letter depends on whose chart you are reading. Our size notes list both so you can match either system.