How to Measure Your Bra Size at Home According to Bra Size Calculator Online

Updated

You can get a working bra size at home with two measurements: a snug underbust and a standing bust. Take both with a soft tape held level, then either run them through the calculator on brametric.com or apply the site's Underbust+4 or Underbust+0 formula by hand. The method works for anyone who can hold a tape measure steady; the only real requirement is that the tape stays horizontal and neither digs in nor hangs loose.

What you need before you start

  • A soft measuring tape (or a string plus a ruler)
  • A mirror, so you can check the tape is level at the back
  • A well-fitting, unpadded bra or no bra at all
  • Your measurements in inches or centimeters — the site's calculator accepts either, but you must specify the unit you used

The two measurements

Standing bust

Measure around the fullest part of your breasts while standing or sitting fully upright. Keep the tape parallel to the floor. Don't compress the breast tissue with the tape, and don't let it sag away from your body either — it should just rest against you.

Snug underbust

Place the tape directly under your bust, in a perfectly horizontal line. It should sit firmly against your ribcage, the way a bra band would feel when it's comfortable — snug, but not pressing into the skin.

Write both numbers down before doing any math.

Turning measurements into a size

The site describes two systems, and they give different band sizes from the same underbust measurement.

Underbust+4 method

Common in the US and UK, and used by many online retailers and brands. Take your snug underbust in inches, round it to the nearest even number, then add 4. For example, a 29" underbust rounds to 30", and adding 4 gives a 34 band.

Underbust+0 method

Use the underbust measurement as-is (rounded to the nearest even number) without adding anything. This is the more direct of the two and is what many modern calculators default to.

Cup size comes from the difference between your bust and band measurements. The site publishes separate band and cup charts, plus a converter that translates your result into US, UK, and other sizing systems — useful because a 34D in one system is not a 34D in another.

Using the online calculator

  1. Take the two measurements as described above.
  2. Enter them into the corresponding fields on the calculator.
  3. Specify whether your numbers are in inches or centimeters.
  4. Read the result, then check the band and cup charts to confirm, and use the converter if you're shopping a brand that sizes differently.

The calculator page requires JavaScript to run, so if the fields don't respond, check that scripts are enabled in your browser.

How to fit a bra once you have a size

A calculated size is a starting point, not a guarantee. The site's fitting guidance covers the checks worth doing before you commit to a style:

  • The band should do most of the support work and sit level all the way around — if it rides up at the back, the band is too loose.
  • The center of the bra should lie flat against your sternum.
  • The cups should contain all breast tissue without gaping or cutting in.
  • Straps should stay put without leaving deep marks.

If the band is right but the cups aren't, adjust cup size rather than band size, and re-check against the cup chart.

Common sticking points

  • Rounding the underbust. Both methods round to the nearest even number, so a 31" underbust becomes 32" before you add anything.
  • Measuring over a padded bra. This inflates the bust measurement and skews the cup calculation.
  • A tape that isn't level. Even a slight tilt at the back changes the number, which is why the mirror matters.
  • Assuming one size fits all brands. The converter exists precisely because sizing systems differ; treat your calculated size as brand-specific once you start shopping.

Once you have a size that passes the fit checks, the site's own next step is to use it to find and buy the style you want — but confirm against each brand's chart before ordering.