Why measuring together is the most reliable method
Every other method on this site works from a clue: a tag, a clothing size, a body shape. Measuring together works from the source. Two numbers from a tape describe the band and cup she needs today, not the size she bought two years ago. That is why the calculator rates it high confidence, alongside a tag from a bra that fits her well.
It also changes the nature of the gift. You lose the surprise of the size. You gain a gift that fits, and the small credit of having asked properly.
How to bring it up
There is no perfect script, but some approaches go better than others. Keep it short, practical and about her:
- “I would like to get you something nice, and I would rather it fit. Would you be up for a two-minute measurement?”
- “I found a calculator that does this in two minutes. Want to try it with me?”
- “I want to buy you a bra you would actually wear. Can you tell me your size, or shall we measure?”
Choose a relaxed moment, not five minutes before you go out. Make it easy to say no. If she would rather measure herself, or would rather just tell you a size, both are fine. The point is a good fit, not a ceremony.
What you need
- A soft measuring tape, the flexible kind used for sewing. A metal tape will not work.
- A thin, unpadded bra, or no bra if she prefers. Avoid padded, push-up or minimizer bras, which change the numbers.
- The calculator open on your phone.
A mirror helps if she is measuring herself. If you are holding the tape, you are the mirror.
Step 1: the snug underbust
She stands straight with arms relaxed and breathes normally. Wrap the tape around her ribcage directly under the bust, where a bra band sits. Pull it snug: firm, flat against the skin, but not digging in.
Your job is the back. Check the tape is level all the way round, because it tends to drift upward behind her. Let her read the number at the front. Round it to the nearest inch.
Step 2: the standing bust
Now move the tape to the fullest part of the bust, still level across the back. This time keep it loose. It should rest on the skin without pressing anything flat. Read the number to the nearest inch or half inch.
Step 3, optional: the leaning bust
She bends forward from the hips until her upper body is roughly parallel to the floor. Measure the fullest part of the bust again, loosely. If you take it and it is larger, enter it as the bust number instead of the standing one, because it often gives a more accurate cup.
That is all the measuring there is. Enter the numbers, in inches or centimeters, and the calculator does the rest.
How the calculator turns two numbers into a size
The underbust, rounded to the nearest inch, sets the band. Bands come in even numbers, so an odd result is rounded down, and the band above is shown as an alternative. The cup is the difference between bust and band, one letter per inch: 3 inches is a C, 4 is a D, 5 is a DD.
For example, an underbust of 32 in and a bust of 36 in gives 32D. An underbust of 33 in and a bust of 37 in gives 32DD, with 34D as the alternative. Those two are sister sizes, with about the same cup volume on a different band.
The full method, with common mistakes, is on the how to measure bra size page.
Common slip-ups
- The tape climbs at the back. Both numbers go up, and the band comes out loose.
- The bust tape is pulled tight. The cup comes out too small.
- She is wearing a padded bra. The cup comes out too large.
- Someone adds 4 inches to the band. An older method did this. It gives loose bands and small cups, so skip it.
What to do with the result
Now you have a size with high confidence. A bra becomes a reasonable gift, with a few sensible limits:
- Choose a style she already wears. A good fit in a t-shirt bra does not guarantee a good fit in a plunge.
- Prefer unlined, seamed cups over molded push-ups if you are choosing the style. They fit natural shapes more easily.
- Check the size system. If you shop a store from another country, convert. A UK 34E is a US 34DDD.
- Keep the tags on until she has tried it with the how a bra should fit.
A tape measure gives an excellent starting size. The final word still belongs to the fitting room, or her bedroom mirror.
If she prefers not to
Some people dislike being measured, for all kinds of reasons, and none of them need explaining. If she says no, take it in your stride. A robe, a soft bralette in S, M or L, pajamas or a gift card all make good gifts without any numbers. So does a voucher for a professional fitting, where she sets the terms. The gift guide has more ideas.
About privacy
The calculator runs in your browser. The measurements are never sent to us or stored anywhere. If you save or share the result, the link carries only the final size in the part of the address after the hash, which browsers do not send to servers. You can close the page and the numbers are gone.
That matters to her, and it should matter to you. It is her information, and she gets to decide who sees it.
Sources & method: sizing rules follow the standard band-and-cup system used by UK, US, AU and EU brands, checked against fitting guides from specialist retailers and fitting communities. How we work.