This guide to how to measure bra size with measuring tape takes about five minutes and one tool: a soft, flexible tape, the sewing kind, not a metal construction tape. You will take two measurements, a snug underbust and a loose standing bust, and those two numbers are everything a bra size calculator needs.
What you need before you start
- A soft measuring tape (paper print-out tapes work if you have no other option, but cloth is easier).
- A mirror, so you can check the tape stays level behind your back.
- No padded bra, or none at all, padding adds volume that is not you.
- Stand naturally and breathe normally. Good posture, not a posed chest-out stance.
How to measure bra size with measuring tape
Step 1: the snug underbust
Wrap the tape around your ribcage directly beneath your breasts, where a bra band would sit. Pull it until it is snug, firm enough to stay in place, not tight enough to dig in. Keep it parallel to the floor all the way round and read the number after breathing out. Example: 32 inches (about 81 cm).
Step 2: the standing bust
Wrap the tape around the fullest part of your bust without pressing in. Let your arms hang relaxed, reaching up or holding the tape lifts the tissue and skews the number. Read where the tape meets. Example: 36 inches (about 91 cm).
Step 3: turn the numbers into a size
Round the underbust to the nearest even number for the band (32 stays 32). Subtract it from the bust for the cup: 36 minus 32 is 4 inches, roughly a D. Result: 32D as a starting size. Enter both numbers in the calculator to get US and EU equivalents automatically.
Measuring tape mistakes that skew your size
- A tilted tape. Dipping at the back adds phantom inches to the bust. Use the mirror.
- Measuring over a padded bra. This inflates the bust and the cup estimate.
- Pulling the underbust too tight. A crushed ribcage reading gives a band you cannot wear. Snug means secure, not painful.
- Holding your breath or standing rigidly. Measure how you actually stand and breathe.
- Mixing units mid-way. Record inches with inches, centimeters with centimeters, or let the calculator handle either.
Inches, centimeters, and converting
One inch is exactly 2.54 centimeters. To go from centimeters to inches, divide by 2.54: an 81 cm underbust is about 32 inches. Going the other way, multiply by 2.54. If reading a centimeter tape in inches feels awkward, skip it, the calculator accepts centimeters directly. Shoppers comparing US and international labels should also see the size converter.
How to read the tape correctly
Tape measures show inches on one edge and centimeters on the other, confirm which edge you are reading before writing anything down, because 32 inches and 32 centimeters describe very different bodies. Read at eye level where the tape meets itself, not at an angle, and note the number immediately; memory is unreliable after the tape comes off. Measure twice: if the two readings differ by more than half an inch, take a third and use the middle value.
Record both numbers like this
Write down the unit with the number every time: “under 32 in, bust 36 in” or “under 81 cm, bust 91 cm”. This prevents the most common recording error, mixing units between the two readings, which produces a nonsense size. Keep the note until the bras arrive; if something fits oddly, the numbers tell you (and any fitter) exactly where you started.
After measuring: confirm the fit
Measurements give a starting size; the mirror and your comfort give the verdict. Check the four fit points, level band, smooth cups, settled centre gore, stable straps, with our fit checker, and read bra basics to understand what each part of the bra should do.
Measuring tape FAQ
How tight should the tape be for the underbust?
Snug enough to stay level on its own, loose enough to breathe and talk comfortably. If it leaves deep marks, it is too tight.
Should arms be up or down for the bust?
Down and relaxed. Arms up lifts the bust and gives a smaller, misleading reading.
Can I measure alone?
Yes, that is what the mirror is for. The one reading worth double-checking is whether the tape is level across your back, which you cannot feel reliably.