What Is Bra Size Calculator Online?

Updated

Bra Size Calculator Online (brametric.com) is a free web tool that turns two body measurements into a bra size. You enter a snug underbust and a standing bust measurement, and the site calculates your band and cup size and converts the result across sizing systems such as US and UK. It suits anyone who wants to check their size at home before buying, but it needs JavaScript enabled to run, and its accuracy depends entirely on how carefully you measure.

What the site actually offers

The page bundles four things in one place:

  • An online calculator at the top of the page that takes your measurements and outputs a size.
  • A measurement guide covering a simple two-measurement method and a more advanced multi-measurement method.
  • A band size chart and a cup size chart for looking up or cross-checking results.
  • A size converter that adjusts the calculation to different national systems, including US and UK.

You can enter measurements in either inches or centimeters, so you are not locked into one unit system.

How the measurement methods differ

The site describes two do-it-yourself approaches, and the choice between them changes your result.

The simple way

You take two measurements:

  1. Standing bust — measure around the fullest part of your bust while standing or sitting fully upright. Keep the tape parallel to the floor, snug but not compressing, and not hanging loose.
  2. Snug underbust — place the tape directly under your bust, perfectly horizontal. It should sit firmly against your ribcage without pressing into the skin, matching the comfort level you would want in a worn bra.

From these two numbers, the site applies one of two sizing systems:

Method Band size rule Where it is common
Underbust + 4 Measure snug underbust in inches, round to the nearest even number, add 4 US and UK, including marketplaces like Amazon and brands such as Natori and Calvin Klein
Underbust + 0 Use the underbust measurement directly as the band size Alternative system, generally used outside the +4 convention

The example the site gives: a snug underbust of 29 inches rounds to the nearest even number and then has 4 added under the +4 method.

The advanced way

The advanced calculator path uses additional measurements beyond the two basics. The page references a "Bra Measurement Guide for the Advanced Calculator" but the excerpt does not detail those extra steps, so treat the advanced route as a more thorough option you would follow directly on the site rather than something to reconstruct from the summary here.

How to fit a bra once you have a size

A calculated size is a starting point, not a guarantee. The site includes a "How to Fit a Bra" section, and the practical checks that matter when you try a bra on are:

  • The band should do most of the support work and sit level all the way around, not ride up at the back.
  • The center gore (the piece between the cups) should sit flat against your chest.
  • The cups should contain your breast tissue without gaping or cutting in.
  • Straps should stay put without digging in; if you need them very tight to feel supported, the band is likely too loose.

If a bra fails these checks, adjust the band size first, then the cup, because band and cup are linked — changing one shifts the other.

What to watch out for

  • JavaScript is required. The page states you need JavaScript enabled to run the calculator, so the tool will not work with scripts blocked.
  • Measurement error dominates the result. The site stresses taking measurements strictly according to the instructions. A tape that is tilted, too tight, or too loose will produce a wrong size no matter which method you pick.
  • The +4 vs +0 choice matters. These two systems can give you different band sizes from the same body, so know which convention the brand you are buying from uses before you order.
  • No pricing or account details are indicated on the page, so there is nothing to suggest paid tiers or login requirements from the material available.

Who this is useful for

Use brametric.com if you want a quick calculation plus reference charts in one place, especially if you shop across US and UK brands and need to convert. If you already know your size and just need a chart, the band and cup tables alone will do. If you are between sizes or have had fitting problems before, work through the "How to Fit a Bra" checks after calculating rather than trusting the number on its own.