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How to measure your bra size

Two measurements, about two minutes. Where the tape goes and how tight you pull it decide whether the answer is right - so this is the part worth getting exactly.

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Before you start

  • A soft tape measure. A fabric or plastic one, not a metal builder's tape.
  • A mirror, so you can see the tape across your back.
  • No padding. Measure without a bra, or in a thin unlined one. A padded cup adds up to two inches to the bust reading.
  • Stand straight, arms relaxed at your sides, breathing normally.

The two measurements

Where to place the tape for each measurementA torso seen from the side, facing right. The upper dashed line runs level through the fullest point of the bust; the lower solid line runs level through the crease directly beneath it, around the ribcage.21BACKFRONT
Underbust - tape snug
Against the ribs, directly beneath the bust. Breathe out.
Bust - tape loose
Around the fullest part, resting rather than pulling.
Both measurements are taken with the tape level all the way round - check the back in a mirror, because a tape that rides up behind you is the single most common cause of a wrong result. Measure in a thin unpadded bra or nothing; a padded cup adds up to two inches to the bust reading and will push the answer two cup letters too high.

1. Underbust - tape snug

Wrap the tape around your ribcage directly under your breasts, where a bra band sits. Breathe out, and pull it snug: as firm as you would want a band to feel, without digging in. This number becomes your band, so it is the one that matters most.

2. Bust - tape loose

Wrap the tape around the fullest part of your bust. Let it rest on you - it should not press anything in or leave a mark. The difference between this number and your band is your cup: one letter for each inch.

That is all the calculator needs. No inches get added to either number.

Keeping the tape level

Both measurements go wrong the same way: the tape rides up at the back. It adds length, and it adds a different amount to each measurement, so the error does not cancel out.

You cannot feel this - your arms are in front of you holding the tape, and the back drifts upward without your noticing. Turn side-on to a mirror and check that the tape runs straight round, parallel to the floor, as in the drawing above.

The six measurements

The calculator's Detailed mode takes up to six measurements instead of two. It follows the method of the A Bra That Fits community, and it is worth the extra few minutes if your breasts are soft or sit low, or if the two-measurement size has not fitted.

Three around the ribcage, in the same place, pulling harder each time:

  • Loose - the tape just resting on you, not pulled at all. Adjusts the cup.
  • Snug - firm but comfortable. This is the one from the quick method, and it sets the band.
  • Tight - as tight as you can pull it, breathing out. Optional: it does not change your size, only the advice on how firm a band will feel.

Three around the bust, with the tape loose, in three positions:

  • Standing - upright, as in the quick method.
  • Leaning - bent forward at the hips until your back is level with the floor, so the breasts hang straight down. Measure around the fullest part.
  • Lying - flat on your back. Measure across the fullest part.
UnderbustMeasure the same spot three times, pulling harder each time.

1 Loose

Tape just resting.

Goes in Underbust, loose

2 Snug

Firm, comfortable.

Goes in Underbust, snug

3 Tight

As tight as it goes.

Goes in Underbust, tight - optional

Looking down on the ribcage. The filled shape is you; the line is the tape. Loose leaves a gap, snug touches all the way round, tight presses in. Snug sets your band and loose adjusts the cup. Tight changes nothing in the size - it tells you how much give your ribcage has - so you can skip it.

BustMeasure three times with the tape loose, in three positions.

1 Standing

Upright, tape loose and level.

Goes in Bust, standing

2 Leaning

Bent forward until your back is level.

Goes in Bust, leaning

3 Lying

Flat on your back.

Goes in Bust, lying

Seen from the side. The dashed line is the tape, always straight around the body at the fullest part. Leaning forward brings all the tissue into the measurement; lying down spreads it.

The leaning measurement is the important one. Standing, softer tissue settles downward and the tape misses some of it; leaning forward brings all of it into the measurement. The tight underbust tells you how much give your ribcage has, which is what decides whether a firm band will feel secure or simply hurt.

What goes wrong

Measuring over a padded bra

Padding inflates the bust reading and the cup with it. A 32-inch ribcage that is a 32D measured bare comes out as a 32DDD over padding.

Holding the underbust tape loose

A slack tape reads a size too big in the band and too small in the cup. The same body measured at 34 instead of 32 becomes a 34B.

Pulling the bust tape tight

Pressing the tape in takes an inch off the bust, and an inch is a whole cup letter. The bust tape rests; only the underbust tape is pulled.

The tape riding up behind you

Adds length to both readings, unevenly. Check it in a mirror rather than by feel.

Questions people actually ask

What do I need to measure my bra size?
A soft tape measure and a mirror. The mirror is not optional if you are on your own - it is the only way to see whether the tape is level across your back, and a tape that rides up behind you is the most common reason for a wrong result.
Should I measure with a bra on?
Without one, or in a thin unlined bra with no padding. Padding can add up to two inches to the bust measurement, and one inch is one cup letter: the same 32-inch ribcage reads as a 32D measured bare and a 32DDD over a padded bra.
How tight should the tape be?
Different for each measurement, and this is the part people get wrong. Under the bust, snug - as firm as you would want a band to feel, breathing out. Around the bust, loose - resting on you without pressing anything in. Pulling the bust tape tight makes the cup come out too small.
Can I measure in centimetres?
Yes. Measure in whichever unit your tape shows and switch the calculator to match - it converts for you. The cup ladder is defined in inches, so the working is shown in inches either way.
What if my breasts are different sizes?
Most people's are. Measure around the fullest point as usual - the tape takes in both - and fit the cup to the larger one. A cup that is slightly roomy on one side is comfortable; one that is too small on the other is not.
Do I need all six measurements?
No. Two measurements give a good starting size for most people, and even in the detailed method the tight underbust is optional - five set the size. The others are worth taking if your breasts are soft or sit low, if your size has changed, or if the two-measurement answer does not fit - the leaning measurement in particular catches tissue a standing one misses.