|Estimated Bra Size||Nearest Sister Sizes|
Click Here for the Most Recent Version
Here are the steps the calculator takes to estimate your bra size.
Differences from the Original GuideThis calculator is not perfect and is meant to be used only as an estimation for your size. A few things have been slightly altered from the original guide linked above.
Update Log3/17/2014 08:30 PM EST - Changed "How to Measure" section to "How to Use." Added subsections "What Your Results Mean" and "What Are Sister Sizes?" Added a sister size chart for reference. Added "Update Log" and "Future Plans" to the "About" section.
3/17/2014 05:50 PM EST - Added KK to the UK Cup size list, as it was mistakenly left out.
3/17/2014 04:30 AM EST - Changed the function that automatically sizes up band sizes of 32 or below so that it now prompts you to consider sister sizing up for comfort. Changed the function that automatically sizes down band sizes of more than 36 so that it now prompts you to consider sizing down for support.
3/17/2014 03:45 AM EST - Bra Size Calculator goes live and is shared on r/abrathatfits.
Future PlansHere are some things that will be incorporated into the calculator later on.
CreditsThis calculator was coded by T. Linton (u/irisflame) with the help and guidance of Joe Saltsman (u/shadowmage).
How to Use
Before You BeginYou should not be wearing a bra when you take these measurements. You should also not distort your breasts in any way while you are taking these measurements. Let them fall naturally.
The calculator takes measurements in inches. It will accept decimals as well, but not fractions.
What You Need
DefinitionsUnderbust - this is the line immediately below where your breast tissue attaches to your chest (called the inframammary fold)
Bust - this is the line across your breasts at their fullest point (usually at or near the nipple)
What Your Results MeanThe calculator is not perfect, but it is fairly accurate. The first bra size it gives you is your estimated bra size. The other two sizes are the nearest sister sizes for your estimated bra size.
If you have a 32 inch or less underbust, you might want to consider sister sizing up for comfort. If your breasts are rather large (GG+) you might need to keep the band size lower for added support. If you have more than a 36 inch underbust, you'll also want to consider sister sizing down for support, since the band sizes greater than 36 tend to be stretchier.
You may need to try on surrounding band and cup sizes in order to find the perfect fit. Remember, not all bras are made with the same cut, so a 34G in one brand might not fit the same as a 34G of another brand. Breast shape also plays a role in determining your bra size. More on shapes will be added at a later time.
What are Sister Sizes?Cup size is entirely dependent on band size. Sister sizes hold the same volume of cup (amount of boob, if you will), but may fit better or worse depending on your preferred band measurement. For every band size you go up, you should go down an equal number of cup sizes, and vice versa.
For the purposes of this guide/calculator, the term "sister size up" means to go up in band size and down in cup size (32G > 34FF) and the term "sister size down" means to go down in band size and up in cup size (32G > 30GG).
Below is a chart with several sister sizes. Each row is a family - all the sizes listed on that row (same color) are sister sizes and have the same cup volume. Note that the further away you go from your estimated bra size, the less likely it is that the bra will fit. This chart is written with the UK sizing method, since it is more consistent.