The hardest part of bra sizing is often not the rule itself. It is knowing where to start. That is especially true when shopping online, where guessing across several sizes can become expensive and frustrating. This bra size calculator is built to narrow that first decision.
After you enter underbust and bust measurements, the page suggests a starting size, band, cup, bust difference, and sister sizes, then adds basic fit-oriented guidance. It is especially useful as a first filter that tells you what to try first and what nearby options may also make sense.
Underbust is the base measurement for the band and often has the biggest influence on support and snugness.
Bust works together with underbust to create the bust difference, which is then used to estimate cup size.
It is best for online shopping, first-time size exploration, or any situation where you want to narrow the try-on range before guessing.
No. It is a starting point, while real comfort still depends on brand shape, fabric, and your own body shape.
They are nearby alternative sizes that help when the recommendation feels close but the band is slightly too tight or too loose.
Use the recommendation as your main starting point, then compare sister sizes, brand charts, and real try-on feedback before deciding.
Calculate your perfect bra size and sister sizes